One very noticeable change to the style of house we have built in Ireland in recent years has been the move away from Bungalows to Dormers and Storey and a half. In the case of a Bungalow or Two Storey it is now recommended to have 12" (300mm) of Fiberglass in your attic. If you insulated your attic a number of years ago, you most likely used either 4" (100mm) or 6" (150mm) Fiberglass. Fiberglass breaks down over time and losses its thermal value as insulation. You can achieve the following U Values using the following thickness in Fibreglass.
|400mm (2x200mm)||0.09 w/m2k|
|300mm (2x150mm)||0.11 w/m2k|
You have a few options. You can top up this insulation by adding insulation to bring it up to the top of the joists and then rolling the balance of the insulation across the joists. This captures any heat lost between the joist and the insulation. You could top up with environment friendly sheepswool or Hemp all of which are on display in our stores. You can use Rockwool which won't breakdown over time and will provide both fire and acoustic values also.
In Dormers or Storey and a half you can fix insulation between the rafters.
Option 1: RafterLoc
Xtratherm RafterLoc is specifically designed for this application. You could use 100mm Polyiso insulation but it is difficult to cut every sheet (1.2m x 2.4m) exactly so that you achieve a good tight fit between the rafters which is essential. The RafterLoc is available in 100mm and 150mm in thickness and is available in slabs 1.2m x 400mm. If high performance felt was used on the roof it is important to leave a space of at least 50mm between it and the insulation as a vapor barrier.
Option 2: Rockwool Flexi
140mm or 100mm Rockwool Flexi can also be used. Like the RafterLoc this product is precut and is as simple as take it out of the pack and put it into place. The unique design of RafterLoc ensures that it will stay in place without having to use staples. It provides a good cosy fit between the rafters allowing for every gap to be filled. Again, as above, a space needs to be left if high performance felt was used. If breathable felt was used it allows you to push the insulation out to the felt. This gives you the advantage of getting as much insulation in between the rafter as possible.
Option 3: Multi foil insulation
Multi foil insulation can be rolled across the rafters and tape the overlaps. The multi foil insulation is based on the principle that the heat radiates off the foil. A mirror effect is probably the best way to describe it. It's fast and very cost effective. Some multi foil product on the market don't carry and IAB certificates and the ones that do insist that you use 125mm fiberglass insulation between the rafters first. With Multi foil insulation one needs to ensure a space of at least 25mm is maintained at both sided of the foil. This can be achieved by counter battening it before the insulated plasterboard slabs are fixed in position. It is our recommendation that you use a multi foil which is rigid, achieves airtightness, and that you us the opportunity to put insulation in between the rafter also.
To get the full value out of your investment in Insulation check out our section on Airtightness.
Email us with your measurements for a competitive price and the best advice. SEI Grants of â‚¬250 are available at present.