Many people are staying in their homes at the moment rather than moving and this has meant that there are more and more extensions going up around the country. This is great in a way as it means that people are starting to treat their houses more like homes and investing in them and their communities.
Most of these extensions will be built using brick and block with a partial fill cavity insulation. Most people will use a phenolic board as it is gives the best insulation per cm of the common insulation materials. These boards are undoubtedly good at insulating, but they do have some issues that you need to be aware of:
1. They are not recyclable. So effectively we are just storing up a waste problem for the future generations to deal with. So I think that their use is quite shortsighted.
2. They need to be fitted correctly. Most builders just put the boards in the cavity and tie them in with the wall ties and possibly a retaining clip. However many do not tape up the joints between the boards. Not taping up and / or not using a retaining clip radically reduces the effectiveness of the boards. Without them them are just knocking around in the vented cavity. This seriously affects their performance in the real world. So we would recommend that you inspect the work done by your builder to ensure that all the insulation is clipped and taped and that there is a continual strip of insulation around all of the house.
3. Buildings are designed to just meet building regulations, so for the sake of a few extra pounds you could specify a 75mm or 100mm board rather than the 50mm. Building in efficiency is so worthwhile for all of us.
4. Look at using low conductivity wall ties (for example Teplo Ties). These stop the cold bridging that occurs with using the conventional steel ties, plus they will not corrode. Using these types of ties allow you to have a larger cavity (to get more insulation in) and also reduce heat loss (tests have shown this can be around a 10% heat saving of the thermal loss through the walls)
We would recommend creating breathable walls (by using products like Durisol, timber frames with breathable insulation – Tradis system for example) as they are generally natural / recycled and recyclable products that are safe for you and the environment. Breathable systems create a better internal environment and can be equally as insulating as the more conventional materials.