Serious about sustainable homes?
Simplicity wins every time.
Its so important to design a building that can actually be built as intended. This sounds obvious but drawings do not cover all aspects of the envelope and typically miss out complicated junctions, which leads to confusion. The Building Contractor / Framer / Fitter must have a clear instruction or detail to work with. Asking them to improvise on site is not practical or economical. The conditioned (warm or heated) envelope must be treated as one entity, a continuous bubble with as few breaching features as possible. This allows any components, insulation and any barriers to be installed smoothly. Smooth assembly methods always result in the most accurate & economical builds.
Focus on structural details that aid building assembly:
* Source materials that are easily available and time proven.
* Avoid over complication and too much tech. New technology is the easiest thing to sell as it quite often provides a false hope that it will improve performance with out having had time to be tested or understood thoroughly. This results in “learning on the move” which is expensive and disrupts the build programme.
* Understanding tolerances and settlement is fundamental to building accuracy and speed, as well as durability. Kit manufacturers should provide builders with tolerance and assembly guides.
* Despite what you may hear, the best methods for sealing envelopes are as follows.
1. Minimise site sealing by framing correctly and insulating with a sprayed breathable PU foam such as Icynene.
2. If using pre-assembled panels or SIPS, then the internal structural sheathing creates the best air barrier along with a gasket or permanently flexible sealant between components. When using home grown timber the tolerances need to be larger due to it being force-grown on slopes (less true). This is why a closed cell PU foam (in a designed gap) is the most suitable seal. Its durable, fast, flexible and insulates where mastic and tape will allow closed or open loop convection.
3. AVCL (Air/Vapour Control layer) also called air-barrier or vapour-check depending on permeability. Extremely labour intensive and requires huge discipline and experience.
4. Spray film AVCL, suits some applications like exposed fibre batts but is expensive and requires a few more years to be proven.
5. Avoid rigid foam insulation (PUR or PIR) apart from specific locations. It is not suited to domestic construction as its labour intensive and typically leads to open loop convection even with an AVCL. The advantages of its better insulating value are lost by the time it has been installed.
6. Tape. Apart from a few specific circumstances its still the most problematic of all. The go-to choice because of clever marketing many years ago, it is an easy product to sell. It’s got a high profit margin and can be shipped from anywhere. They come with very good glues and strong backers now but will never cope fully with damp, cold & dust. Remains the number one cause of air-barrier failure.
Unbridged Envelope, Heat Recovery Ventilation, Shading, Thermal Mass & Simple Care = Minimal Energy.
A truly sustainable home ideally consumes no more energy to build or run than it captures, and the building products & process leave little or no dent in our environment or health. It’s a good concept and congratulations to those who have achieved this, however it is too much to ask of every new-build as it would seem unrealistic as most challenges vary depending on the environment, resources & Law. You CAN get close to this with impressive results by avoiding gimmicks and sticking to basic building physics. Aim for the following as a starting point:
* Less than 3% Cold bridging.
* Air-tightness below 0.6 ACH.
* MVHR (ACTUAL) efficiency 90% +. Capable of reducing energy demands by around 30%
* Carefully sized & oriented glazing with High-Sun Shading.
* Sensible thermal mass distribution. Mineral floors and double layer plasterboard are a cost & space friendly whilst improving fire resistance.
* Avoid heating systems on the 1st Floor or above other than towel rails etc.
* Avoid FROGs (finished room above garage). Awkward features like this always require additional energy.
Certified & Proven
All good Sustainable Buildings require measurement, testing and certification. On top of standard documentation the following will be required.
* Calculation for energy efficiency such as PHPP or HOT2000. SAP calculations are not accurate enough.
* MVHR Flow Schedule.
* Mid-build Air-tightness Test Report (result below 0.4 ACH).
* Completion Air-tightness Test Report (result below 0.6 ACH).
* MVHR commissioning report + Warranty.
* Heating system commissioning report + Warranty.
* Renewable energy commissioning report + Warranty.
As well as Certification you will need evidence that the methods, equipment, products and professionals can achieve what they claim.
Ask to see buildings and systems in operation and evidence of performance.
Most importantly when it comes to design, specification & installation there is no replacement for time served hands-on experience. You cannot buy this or substitute it with graphics and trade association membership.
Seek referrals from other satisfied customers.
Well designed drainage & ventilation = long lasting structures.
We take for granted that our engineers get structural load calculations right, and the industry has come a long way in fire prevention. The most common causes of building deterioration are moisture bottle-necking and poor airflow along with cold bridging. This is mainly from lack of understanding of moisture & air movement at the design stage. Site experience in dealing with old/new, good/bad, structures is a huge advantage when designing-in durability. Understanding the movement of air and water through structures is fundamental to ensuring long term building integrity.
* Good Whole-House-Ventilation such as MVHR ensures essential air management.
* Breathable spray foams minimise cold-bridging while ensuring air-tightness when used with the correct framing.
* Thorough design & install of membranes if using fibrous insulation, avoid using tape.
* Identify all elements that require drip control or cavities to prevent moisture build-up.
* NEVER try to stop water without giving it somewhere else to go.
* Avoid lamination of moisture resistant materials.
* Use Structural air-barriers instead of membranes where possible.
* All services must be serviceable including MVHR. Ducting must be accessible/cleanable steel or semi-rigid.
Affordable / Economic
Design-out potential assembly conflicts and remove unnecessary products & gimmicks.
Minimise heating requirement through an effective envelope with MVHR and achieve little or no heating costs.
Invest in preparation, homework & practice (regardless of wether you are a professional or a self-builder).
Low energy, durable homes don’t have to cost more to build than conventional. Excessive build & running costs are usually down to the following;
* Compound measuring instead of assembling by Datum.
* Under Quoting – Many providers miss elements out to keep the quotes low then offer to introduce them as extras later.
* Awkward or incomplete design details.
* Excessive glazing.
* Hi-spec, labour intensive products like rigid foiled insulation and air-tightness tapes.
* Specifying of unnecessary heating.
* Lack of experience and knowledge in efficient envelopes (especially air-tightness).
* Poor access, untidy sites & wasted/damaged materials. For your build to be cost effective, the build needs to be smooth. This means clear work areas, organised space, platform access to high areas, good lighting, minimum waste and disciplined scheduling.
* Remember that making design changes during the build costs money & time.
Healthy & Comfortable
Ventilation & safe building products = good air quality.
Most of us who take building seriously are more than aware that air quality has rapidly declined over the last 50 years. Some improvements were made in the form of common bathroom extracts and trickle vents, but neither work particularly well and have no energy recovery and so expel airborne energy. Since early use in Canada in the 70’s, MVHR has long been the common sense option for new-builds in countries where building physics is widely understood. The UK has taken a lot longer but things are finally moving. The MVHR industry is fairly young so we must continue to closely observe progress. The key to a good system lies in design and planning with strong focus on ducting. A good MVHR system will provide continuous fresh air, remove contaminants and recover most airborne energy.
Good Ventilation units will include Active Defrosting, Summer Bypass, and an option for Pollen Filtering. Try you’re best to avoid products that leak chemicals such as MDF furniture etc. More watered plants indoors will also help balance your indoor environment.
warmth, space, air, light & security = comfort.
Nearly all of us have grown used to, expect, or would like warmth, space, light & security when needed in our climate.
Good warmth & light in particular, are fairly recent luxuries ,while air quality has generally deteriorated.
In order to keep these comforts and improve air-quality everyone will need a better understanding of design, & construction practices.