9. Choosing a Building System
What is a 'Building System'?
Choosing a ‘Building System’ suitable for your house is a key stage of the design process. Usually considered at the outset, the choice of a ‘System’ will be the product of some careful thought.
A ‘Building System’ commonly refers to the essential components that when combined make-up the method by and the materials from which the house will be constructed.
The main part of the system will naturally be the walls of the house - but the roof, ground floor and interior will also be related.
The components of a ‘Building System’ are its:
- Structure: The means by which the building ‘stays up’.
- Cladding: The material or combination of materials that protects your home from the elements.
- Insulation: The material included as part of the system that keeps your house from losing heat.
The completed outside of the building is often termed as the ‘Building Envelope’ - and its a useful way to think about how your house works.
Choosing the appropriate system is important because it influences the choices you make about the building materials you select.
It’s very tempting to choose a system ‘off the cuff’. You might have seen a system in a magazine or on a tv programme and simply liked it’s appearance or as a complement to your life-style. The temptation should be avoided!
Choosing the right Building System for you is not unlike buying a new car. Amongst several in the show room, one car will be the most suitable for you. In the same way you do your research in buying a car, drawing up a list of your needs an preferences will be useful to the decision making process. Here are some of the issues you might consider:
• Cost: Top of the list: Not surprisingly, the price of the system should match your budget. It’s not always straightforward though - for example buying a prefabricated system might be expensive but that might be outweighed by the cost of maintaining a workforce on site over a long period building from scratch.
• Your ‘Green’ ambition: Sometimes making the ‘environmental / eco’ choice can be the more expensive. Think hard about how you want to be sustainable and the way that the house you build will fit your ideal. What’s important to you? Are some material choices more significant than others? Everyone will have different priorities. Almost certainly be prepared to compromise!
Your way of life might prove a factor in the system you select. For example, if you use a heating system, then how quickly the house warms up will depend largely on the building system you choose. If you’re out a lot and come back from work and want to get warm quickly, perhaps look at a lightweight timber frame system; on the other hand, if you spend a lot of the day in the house, go for a heavyweight wall system - it takes slightly longer to heat up at the outset, but takes much longer to cool. And then there are the stations in between………
How long can you allow for building? If you have to live in caravan onsite, you might make the choice based on build-speed. Some systems are quicker to construct than others.
In all the above, talk to your building designer. Architects are very experienced in making construction choices so involving a professional at an early stage will make sense.
The Structure
The ‘structure’ of the house is the medium through which the load of the building (eg the ‘weight’) is transmitted through the construction to the ground below. Making up the loading will be elements such as the cladding, roofing, interior walls, floors and ceilings, electrics and ventilation systems.
In normal domestic housing there are two broad categories of structural system:
- Load-bearing wall systems - usually including masonry (eg the conventional ‘Cavity Wall’) but also timber
- Building frame systems - usually timber, but metal frames can also be used.
The structural technique usually determines the categorisation of the system as either ‘Bearing Wall’ or ‘Timber Frame’. We’ll use those categorisations when we look at the systems in more detail below.
This illustration shows how the two basic systems transfer loading:
- The bearing wall building on the left (brick wall) delivers the loading vertically through the most direct route to the ground
- The basic timber frame on the right directs the load by transferring through ‘beams’ towards and down through ‘columns’ - hence the system’s common moniker ‘Column and Beam’.
Cladding
‘Cladding’ can be a number of materials or a number of materials combined, all of which when assembled form the outside layer of the building that resists the ‘Elements’ in the form of rain, snow, wind and sun.
The cladding material(s) you choose will usually be determined in large part by what the local authority planners allow. Most claddings such as brick, render and timber are traditional and can be combined with most structural systems.
Insulation
Insulation is an essential part of every building design and specification. Year on year, the government has upped the game with insulation standards through the auspices of the Building Regulations. Insulation is the main tool we have to reduce the amount of energy we consume heating our houses.
There are a variety of insulation materials in the market. They are categorised by the source of the material:
‘Natural’ / Organic insulation materials, favoured by ‘green’ architects, include:
- Cellulose
- Cork
- Wood fibre
- Hemp
- Hempcrete
- Flax
- Sheeps wool
Mineral insulation materials:
- Rock wool
- Glass mineral wool
- Cellular or foamed glass
- Aerogel
Oil-based insulation materials: Include:
- Expanded Polystyrene (EPS)
- Extruded Polysyrene (XPS)
- Rigid Polyurethane (PUR/PIR)
- Phenolic foam
Choosing an insulation material isn’t straightforward and has much to do with context. Your architect will guide you through the alternatives but in order of environmental preference choose (1) Organic insulation (2) or Mineral insulation followed by (3) Oil-based insulation materials which Oil-based / plastic materials usually have the largest environmental footprint but are the most efficient in terms of space.
What is it? : Key Component Zones
- A Cavity Wall consists of two masonry leaves separated by a cavity filled with insulation. The leaves are connected by wall ties.
- The leaves can be from brick stone or concrete block
- The outer masonry leaf protects the vulnerable insulation and inner structural from the weather and damp
Background / History of the System
- Most houses built now are constructed using cavity walls. They are the clear favourite of the volume house builders. If you buy a house, the chances are that it will be a cavity wall type. The use of cavity walls dates from the early-20th century when they were introduced to combat damp penetration. Prior to that, all walls were solid, usually of the 9 inch variety. Many people live in houses that have solid walls. Most houses built since the 1930s have cavity walls, but not all of them have insulation inside. Insulation was first introduced into the Building Regulations in 1976.
Building the System
- Cavity wall construction is labour intensive. What it delivers in flexibility of design is balanced by the time it takes for bricklayers to glue small fired clay or concrete components together using mortar or thin-joint adhesive. Both leaves have to be built at the same time and linked together by wall ties. Insulation too must be built-in as part of the process.
Finishes
- The external leaf can be left as brick as in most houses OR
- If using concrete block, it presents an accommodating background from which to mount a myriad of finishes or it can be rendered directly
Overall Insulation Potential
- To insulate properly, cavity walls need to have very wide cavities. This is not always structurally possible. The size of the cavity is the obstacle.
Thermal Bridging
- Wall ties cause prolific thermal bridging. Lintels are a risk area.
Ease of air-sealing
- Wet plaster ‘parge coat’ is common on the inside leaf - this, rather than plasterboard, provides a good standard of air-tightness. However, wall penetrations for services and especially around window openings are vulnerable points and require very high standards of workmanship - which is not always available.
Availability of Thermal Mass
- If plaster is applied directly to the internal blockwork, then there is a good extent of exposed thermal mass.
Insulation types available
- Ideally, the cavity should be ‘partial fill’ rather than ‘full filled’ - leaving a small air cavity at the front between the outer skin and the insulation. This means that the insulation needs to come in slab (‘batts’) format and fixed against the inner leaf of the wall.
Build Speed
- Slow. Labour intensive. Affected by inclement weather.
Builder Familiarity
- Builders are very familiar with cavity wall construction
Green Rating: Low
- + Bricks are very durable
- + Brick clay is a plentiful resource
- - Bricks have a very high embodied energy from firing.
- - Concrete blocks use cement and aggregate - both have an environmental impact
- - Road transport of bricks and blocks adds to embodied energy
- - Most suitable insulation types are oil-based e.g. Polystyrene, Polyurethane.
Opportunities for improving Green Rating
- Use reclaimed bricks
- Use lime mortar rather than cement mortar. Bricks can then be recycled again
- Use Cellular Clay Blocks for the internal leaf
Notes
- Talk to manufacturers / suppliers about your needs
Cost
- Relatively low cost.
What is it? : Key Component Zones
- A single leaf (‘Monolithic’) form of construction. The structural element is the clay block wall which is clad with insulation and finished to the exterior with either render or timber/rainscreen cladding.
Background / History of the System
- Clay blocks are a very common building system on the continent. The system has been tried and tested for decades. Blocks are extruded with vertical perforations. Sawdust particles are mixed in with the clay which, during firing, burn away to give a micro-porous structure. The combination of voids and pores gives the blocks their thermal properties.
Building the System
- Monolithic clay block walls are significantly quicker to build than cavity walls. Blocks avoid standard mortar joints by using a thin bed adhesive system on horizontal courses. Vertical joints are interlocked between blocks.
Finishes
- The clay blocks, themselves insulation, can either be rendered directly OR
- Alternatively, slab insulation is included and in turn rendered or clad with timber or a rain screen cladding system.
Overall Insulation Potential
- A single leaf (‘Monolithic’) form of construction. The structural element is the clay block wall which is clad with insulation and finished to the exterior with either render or timber/rainscreen cladding.
Thermal Bridging
- Virtually no thermal bridging.
Ease of air-sealing
- Wet plaster ‘parge coat’ is common on the inside of the blockwork - this, rather than plasterboard, provides a good standard of air-tightness. However, wall penetrations for services and especially around window openings are vulnerable points and require very high standards of workmanship - which is not always available.
Availability of Thermal Mass
- If plaster is applied directly to the internal blockwork, then there is a good extent of exposed thermal mass.
Insulation types available
- Only ‘rigid’ insulation, ideally wood fibre boarding, which is fixed to the exterior face of the blocks.
Build Speed
- Labour intensive but a single leaf wall is significantly quicker than a cavity.
- The less water involved means quicker drying-out times
Builder Familiarity
- Relatively low. Skills training is sometimes available from suppliers
Green Rating with timber, render, tile cladding: High
Green Rating with with brick: Medium
- + Blocks are very durable
- + Clay is a plentiful resource
- - A modicum of embodied energy from firing the blocks, though less so than bricks (see above)
- - Road transport of blocks adds to embodied energy.
Notes
- Care needs to be taken on site - blocks are easily damaged ahead of construction
- Talk to manufacturers / suppliers about your needs
Cost
- Material costs can be higher, but rapid assembly reduces labour costs
What is it?
- A cross-laminated timber panel (aka 'Crosslam' or 'Xlam') is a ‘monolithic’ form of construction that uses timber to form load-bearing solid timber wall, floor and roof panels. Openings for doors and windows are incorporated within the panels. In many cases only insulation and cladding is added to the external face. Another distinct feature of CLT is its high resistance to fire - a problem that dogs other timber frame systems.
Background / History of the System
- Only relatively recently introduced into the UK, CLT has its origins in the traditional timber technologies of central Europe and Scandinavia. A small number of self-build houses have taken up the system, but the bigger areas of progress have been in public housing and schools. Effectively it is just taking to mainstream construction.
Key Component Zones
Building the System
- Pre-fabricated to high factory tolerances, the completed panels are transported, usually from Europe, to the site in the UK. There the panels are rapidly erected and finished with external cladding. Internally the panels can be left as natural wood or finished with an application of plaster/clay/mineral board. Like other pre-fabricated panels, CLT needs a good deal of careful planning and co-ordination before work starts on site.
Finishes
- A wide range of cladding is available such as timber and render.
- Internally the wall can be left bare or plaster/clay/mineral boarding can be fixed.
Overall Insulation Potential
- CLT has a similar thermal insulation performance to light weight concrete blocks.
Thermal Bridging
- Neglible
Ease of air-sealing
- High levels of air-sealing are inherent in factory-produced units and installed by specialist contractors on site.
Availability of Thermal Mass
- If the internal face is left as bare wood, there is a fair amount of thermal mass available.
Insulation types available
- Rigid insulation such as wood fibre boards can be mechanically fixed, or a non-structural wood frame can be used to include flexible insulation.
Build Speed
- Erection is performed on site within 3-4 days.
Builder Familiarity
- The manufacturers usually provide their own erectors.
Green Rating: Medium
- + Timber has near-perfect eco-credentials
- + High levels of production make high building performance more easily attainable.
- + Waste is significantly reduced on site
- + CLT is vapour-permeable and can contribute to the ‘breathing wall’ principle.
- - Significant embodied energy can be added through transportation, particularly if imported from overseas.
Opportunities for improving Green Rating
- Specify a UK-based manufacturer, if available, to lessen transport energy.
- Use reclaimed bricks if contemplating brick cladding.
- Use lime mortar rather than cement mortar. Bricks can then be recycled again
- Add thermal mass to the building through using stone/tile flooring
Notes
- Talk to manufacturers / suppliers about your needs
Cost
- High
What is it?
- Insulating concrete form or insulated concrete form (ICF) is a system of formwork for reinforced concrete usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The units lock together somewhat like Lego bricks and create a form for the structural walls or floors of a building.
- Whereas the more common foam and polystyrene formwork materials are of high environmental impact, there is a type available in the UK made using recycled timber.
Background / History of the System
- The ICF construction technique was first developed in Europe following World War II as an inexpensive and durable way to rebuild damaged structures. The adoption of ICF construction has steadily increased since the 1970s. In the UK there are many commercial buildings as well as private houses that have been successfully constructed.
Key Component Zones
Building the System
- Reinforcing steel bars are usually placed inside the forms before concrete is poured to give the concrete strength, similar to bridges and high-rise buildings made of reinforced concrete. Like other concrete formwork, the forms are filled with concrete in "lifts" to manage the concrete pressure and reduce the risk of blowouts.
- After the concrete has cured, the forms are left in place permanently.
Finishes
Overall Insulation Potential
- Conventional expanded polystyrene formwork currently available provides good performance. The best performance though is from using the more developed EPS by BASF known as Neopor.
- Recycled timber formwork with a material such as made by the UK firm Durisol, can achieve a Passivhaus standard of insulation
Thermal Bridging
- None/minimal. Thermal bridging does not occur in the actual walling, but might where openings occur. The extent of bridging can be resolved, as usual, by good detailing and workmanship.
Ease of air-sealing
- Good. Air-sealing is inherent in this construction type.
Availability of Thermal Mass
- Practically none. Thermal mass is available, but only in the core concrete which is sandwiched between slabs of insulation. Because of this, the thermal mass must be regarded as inaccessible - contrary to the claims of the manufacturers.
- The construction typically offers up to around 6 hours worth of thermal buffering/ decrement delay available - so e.g. maximum temperatures on the outside are followed on the inside 6 hours later
Insulation types available
- Foam and expanded polystyrene are by far the most common available. Green builders would be looking at using the slightly more sustainable Durisol equivalent (though it includes polyurethane foam).
Build Speed
- Quick.
Builder Familiarity
- Most builders will be unfamiliar with ICF, but it is easy to learn. If you still have a Lego set….
Green Rating with foam or polystyrene formwork: Very Low
- - Virtually nothing can be described as being of low environmental impact. Concrete is high embodied energy. Foam is a petrochemical product and expanded polystyrene is environmentally hostile both during production and in disposal. The seas are full of it.
Green Rating with recycled timber formwork: Low
- + Timber has near-perfect eco-credentials
- - Uses polyurethane foam for much of the insulation
- - Thermal mass needs adding somewhere else.
- - Uses concrete as the structural element
Opportunities for improving Green Rating
- Avoid petrochemical products if possible
- Use reclaimed bricks if contemplating brick cladding.
- Use lime mortar rather than cement mortar. Bricks can then be recycled again
- Add thermal mass to the building through using stone/tile flooring
Notes
- Talk to manufacturers / suppliers about your needs
Cost
- Around a 10% premium or more over standard brick & block cavity wall construction.
What is it?
- ‘Hempcrete’ is the popular term for a hemp-lime composite building material. It is created by wet-mixing the chopped woody stem of the hemp plant (hemp shiv) with a lime-based binder to create a material than can be cast into moulds. this forms a non-load-bearing, vapour permeable and insulting material than can be used to form walls, floor slabs, ceilings and roof insulation.
- A Hempcrete wall is made from two components. Hempcrete which, when hardened, provides the mass around the timber frame which provides the structure. The effect, though, is monolithic and no extra insulation needs to be added. When dried, finishes can be applied to the external and internal walls.
Background / History of the System
- Historically hemp has a long record of being including in products such as rope and sailcloth as well as oils and, notoriously, stuff set alight and inhaled slowly.
- Hempcrete was developed in France in the 1980s. Since then it has gradually spread worldwide.
- In the UK, the upsurge in hemp construction occurred after the UK Gov funded a number of hemp building projects.
Key Component Zones
Building the System
- Cast-in-situ hempcrete refers to mixing hempcrete on-site and casting it into moulds made from shuttering, to form the walls, floor or roof. Because hempcrete is non-load-bearing it is always cast around a a timber frame which provides the main load-bearing structure.
Finishes
- Hempcrete’s simplest finish is lime render on the outside with lime plaster on the inside. Though other finishes are perfectly possible, they tend to be rather complicated.
Overall Insulation Potential
- Can provide very high levels of insulation depending on thickness.
Thermal Bridging
- Can be easily designed-out
Ease of air-sealing
- Very easy
Availability of Thermal Mass
- Thermal Mass is integral to the material when plastered.
Insulation types available
- Insulation is inherent to the material
Build Speed
- Pretty slow. 6-8 weeks before finishes can be applied
Builder Familiarity
- Unfamiliar. Requires specialist sub-contractor, but can be easily learnt.
Green Rating: Medium
- + Hemp is a quick growing renewable crop. It absorbs CO2 during growth
- + Timber (in the construction) has excellent environmental qualities
- + + Good for lime or clay plaster
- +- Lime has high embodied energy
Notes
- Talk to manufacturers / suppliers about your needs
Cost
- Similar or slightly higher than brick-cavity-block wall construction. Main contractors will likely add a premium for unfamiliarity.
What is it? : Key Component Zones
- The structure of the building is made up of timber stud framework which is infilled with insulation and clad with boarding on the inside and with a variety of possible claddings on the outside - including timber, brick or tiles. An open-frame is on where the timber structure is first erected followed by infilling and cladding.
- In the variety of open-frame that includes wood-fibre insulation, the racking board is relocated from cladding the outside of the frame through to the inside. Then together with flexible insulation infilling the stud frame and timber fibre boarding added to the outside, a build-up of considerable depth provides high levels of insulation.
- Another key feature of a timber fibre build-up is that it provides for a ‘breathing wall’ - where moisture is absorbed into the fabric of the wall rather than condensing on the inside. (Note here the lack of a vapour barrier common in all other forms of timber frame.) This avoids mould and other factors that risk the health of the inhabitants.
- Significantly too, wood fibre provides the only way that a lightweight timber-framed house can reduce the degree of over-heating of rooms. As our summers become hotter, this feature will be increasingly important in the UK as, particularly in the south of England, temperatures are looking to rise to Mediterranean-like peaks from the 2040s onwards.
- Timber frame is second only to cavity wall in popularity to the volume builders. To self-builders it is a clear favourite. Nearly all domestic in construction in the North America is timber frame, but it has lagged in the UK due to the native lack of timber availability. The advantage of a timber frame is that much of it can be prefabricated and delivered to site and rapidly assembled.
- Timber fibre has been developed into insulation products throughout Europe in the last couple of decades. Timber rich countries of Germany and Austria have led the way in producing a product with high performance and very low environmental impact.
Background / History of the System
Building the System
- An open timber frame is quickly assembled as the complete structure ahead of including insulation and adding the external cladding and internal boarding. In most cases it is delivered to site prefabricated and craned into position. It provides a large degree of flexibility in assembly and changes on-site. It is easy to accommodate electrical and plumbing services within the overall building envelope.
Finishes
- Volume builders would add a brick outer leaf - but a whole range of ‘greener’ cladding is available such as timber and render.
- Internally the wall is best clad with mineral board or clayboard.
Overall Insulation Potential
- Standard section timber stud is unlikely to accommodate sufficient insulation within its thickness. This will necessitate additional insulation to the outside of the studwork - or the use of a much deeper section structural timber system such as an ‘I-Joist’
Thermal Bridging
- Low, particularly where an extra external layer of insulation is applied.
Ease of air-sealing
- The air-tightness layer is usually performed by the timber board used as ‘racking’ on the inside of the stud wall. Conventionally joints are taped - but 'sprayed-on' membranes are becoming available which will cut down labour time and possibly increase protection
Availability of Thermal Mass
- Wood fibre will provide an adequate degree of thermal mass
Insulation types available
- Flexible insulation between the studs and rigid wood fibre boards as required on the outside of the studs. It’s a good way of building up very high levels of insulation potential.
Build Speed
- The stud frame can be assembled rapidly. Overall time is determined by cladding format.
Builder Familiarity
- Builders are very familiar with timber frame construction
Green Rating with timber, render, tile cladding: Very high
Green Rating with with brick: Medium
- + Timber has near-perfect eco-credentials
- + Timber frames can use a wide range of environmental preferable insulation materials.
- + Wood fibre insulaiton provides excellent protection against overheating in the summer
- - A modicum of embodied energy from the wood fibre production process
- - Can be compromised if the structural timber is unnecessarily treated with chemicals.
- - Rigid wood fibre needs careful handling to prevent damage
- Talk to manufacturers / suppliers about your needs
- More expensive than cavity wall construction.
- Currently slightly more expensive than conventional open-frame construction
Notes
Cost
- The structure of the building is made up of timber stud framework which is infilled w ith insulation and clad with boarding on the inside and with a variety of possible claddings on the outside - including timber, brick or tiles. An open-frame is on where the timber structure is first erected followed by infilling and cladding.
- Timber frame is second only to cavity wall in popularity to the volume builders. To self-builders it is a clear favourite. Nearly all domestic in construction in the North America is timber frame, but it has lagged in the UK due to the native lack of timber availability. The advantage of a timber frame is that much of it can be prefabricated and delivered to site and rapidly assembled.
- The structure of the building is made up of timber stud framework which is infilled with insulation and clad with boarding on the inside and with a variety of possible claddings on the outside - including timber, brick or tiles. An open-frame is one where the timber structure is first erected followed by infilling and cladding.
- An open timber frame is quickly assembled as the complete structure ahead of including insulation and adding the external cladding and internal boarding. In most cases it is delivered to site prefabricated and craned into position. It provides a large degree of flexibility in assembly and changes on-site. It is easy to accommodate electrical and plumbing services within the overall building envelope.
- Volume builders routinely add a brick outer leaf - but a whole range of ‘greener’ cladding is available such as timber and render.
- Internally the wall is clad with plasterboard - but other materials with a lesser environmental impact, such mineral board or clayboard, are available.
- Standard section timber stud is unlikely to accommodate sufficient insulation within its thickness. This will necessitate additional insulation to the outside of the studwork - or the use of a much deeper section structural timber system such as an ‘I-Joist’
- Low, particularly where an extra external layer of insulation is applied.
- The air-tightness layer is increasingly performed by the combining of two functions into one membrane, the Air and Vapour Control Layer (AVCL) on the inside of the stud wall. Membranes tend to include many joints which will need sealed by specialist tapes. It’s quite labour intensive and getting through tests can be problematic, particularly at the higher end of air-standards.
- There is very little thermal mass available in timber-framed construction - though the internal plaster/clay-boarding will provide a smidgen.
- Flexible insulation between the studs and rigid wood-fibre boards as required on the outside of the studs. It’s a good way of building up very high levels of insulation potential.
- The stud frame can be assembled rapidly. Overall time is determined by cladding format.
- Builders are very familiar with timber frame construction
- + Timber has near-perfect eco-credentials
- + Timber frames can use a wide range of environmental preferable insulation materials.
- - Can be compromised if the structural timber is unnecessarily treated with chemicals.
- - Thermal mass needs adding somewhere else.
-
Notes
- Talk to manufacturers / suppliers about your needs
-
Cost
- Similar or slightly lower than cavity wall construction.
What is it?
Background / History of the System
Key Component Zones
Building the System
Finishes
Overall Insulation Potential
Thermal Bridging
Ease of air-sealing
Availability of Thermal Mass
Insulation types available
Build Speed
Builder Familiarity
Green Rating with timber, render, tile cladding: High
Green Rating with with brick: Medium
What is it? Key Component Zones
- A SIP is pre-fabricated panel sandwich of two layers of Oriented Strand Board (OSB) bonded to a filling of polyurethane insulation (PUR). Unlike timber frame structures, the SIP is both panel and structure together. Relatively thin walls are achievable while providing substantial insulation capacity
Background / History of the System
- Structurally Insulated Panels (SIPs) originated in the USA. SIPs have been building up a market in mainstream construction in the UK for over 10 years. Improved systems of bonding and CFC-free cores have developed to a point where SIPs are making significant inroads to areas which were dominated by traditional timber frame construction.
Building the System
- Pre-fabrication ensures that SIPs are manufactured to a high quality in the factory before delivery by lorry to site. Panels are erected as roof and walls using a crane. Finishes and services are installed by another contractor. Small diameter services can be included within the build, but larger conduits and ducts will be surface mounted. Ensure that everything is planned in detail before reaching factory production. Once the panels have reached site, there’s no changing of the plans
Finishes
- Through habit, there is still a preference for a brick outer leaf - but a whole range of ‘greener’ cladding is available such as timber and render.
- Internally the wall is clad with plaster/clay/mineral board in one layer with a service zone or two layers to accommodate services when chased-out.
Overview
In terms of a Green system solution, SIPs score on a number of grounds including the potential for highly insulated air-tight construction. The system is let-down by the petrochemical insulation at the core of the product. Adding a brick skin (instead of low impact alternatives) only compounds the problem.
Overall Insulation Potential
Thermal Bridging
- Very low. Some thermal bridging at the joints.
Ease of air-sealing
- The method of assembly of SIPs offers an easy route to air-sealing.
Availability of Thermal Mass
- There is very little thermal mass available in timber-framed construction - though the internal plaster/clay-boarding will provide some.
Insulation types available
- Because of the nature of factory production, only polyurethane insulation is available
Build Speed
- The SIPs can be assembled rapidly over around a week. Overall time is determined by cladding format.
Builder Familiarity
- Though easy to assemble, SIPs are usually installed by specialist sub-contractors.
Green Rating with timber, render, tile cladding: High
Green Rating with brick: Medium
- + Timber has near-perfect eco-credentials
- + High air-tightness standards are easily reached.
- - Choice of insulation restricted to oil-based and high embodied energy urethanes
- - Thermal mass needs adding somewhere else.
- - Transport to site adds to embodied energy
Opportunities for improving Green Rating
- Use reclaimed bricks if contemplating brick cladding.
- Use lime mortar rather than cement mortar. Bricks can then be recycled again
- Add thermal mass to the building through using stone/tile flooring
Notes
- Talk to manufacturers / suppliers about your needs
Cost
- More expensive than timber frame - but expense can be retrieved through much shorter build time.
What is it?
- Closed-Panel Timber Frame is a good example pre-fabrication or Modern Methods of Construction (MMC). It is closely related to the open-frame principle but where the structure is incorporated within a pre-fabricated panel. The panels are made and assembled in a factory from where they are transported to site. Nearly everything including insulation, doors, windows, services conduits can be pre-fitted. By assembling in the factory. much greater attention can be paid to detailing with tighter margins of error - useful when constructing a high performance building.
Background / History of the System
- Popular in Scandinavia and Germany where timber products are natural to the construction economy, it is taking time for the idea to penetrate the UK market, but products are becoming easily available from European, particularly Baltic, manufacturers exporting to the UK market. Product quality is generally very high. The downside is that after fabrication, it is nearly impossible to change plans on site - so detailed design has to be wrapped-up before getting to the factory.
Key Component Zones
Building the System
- The essence of Close-Panel Timber Frame construction is it’s factory base. Nearly everything is pre-fabricated in highly controlled conditions. Panels are then delivered to site by lorry and craned into place.
Finishes
- A wide range of cladding is available such as timber and render.
- Internally the wall is usually clad with plasterboard.
Overall Insulation Potential
- The larger dimensions required for high standards of insulation are easily available in this construction type.
Thermal Bridging
- Low, though the timber structure itself is the weak point
Ease of air-sealing
- High levels of air-sealing are inherent in factory-produced units and installed by specialist contractors on site.
Availability of Thermal Mass
- There is very little thermal mass available in timber-framed construction - though the internal plasterboard might make a small contribution.
Insulation types available
- Although having the capacity to include the ‘greener’ types of insulation, in practice the manufacturers will opt for glass or mineral fibre.
Build Speed
- Erection is performed on site within 3-4 days.
Builder Familiarity
- Specialist fabricators are required - usually the panel supplier.
Green Rating: Medium
- + Timber has near-perfect eco-credentials
- + Waste is significantly reduced on site
- - Current types of insulation installed are not particularly Green.
- - Significant embodied energy can be added through transportation, particularly if imported from overseas.
- - Can be compromised if the timber is unnecessarily treated with chemicals.
Opportunities for improving Green Rating
- Specify a UK-based manufacturer, if available, to lessen transport energy.
- Use reclaimed bricks if contemplating brick cladding.
- Use lime mortar rather than cement mortar. Bricks can then be recycled again
- Add thermal mass to the building through using stone/tile flooring
Notes
- Talk to manufacturers / suppliers about your needs
Cost
- High