Week 7 Finishing the Roof

Posted by on May 6, 2013 in Warm EnerPHit office | Comments Off on Week 7 Finishing the Roof

Since the last air test the team have been concentrating on finishing the super insulated roof. Happily after the initial setback with the tape the job has gone pretty smoothly since then! It’s been a big job though and there is a palpable sense of relief to be ready to move on to the next task.




The insulation for the roof is made up of a mix of 50mm slabs and 200mm  mineral wool rolls. They’re both doing the same job up on the roof, but the two are required to deal with the spaces create by the I-beams: the slabs go at top and bottom, and the roll in the middle. At least that was the theory, in practice the wonky roof has meant

that we’ve had a gap under the I beams, up to 25mm.  Since it is important to avoid air gaps in the insulation, we’ve put 350mm into the 300-325mm gap: start at 50mm; then the 200 squishy quilt, then another 50mm to tuck under the flanges of the I beam, and then another 50mm between the flanges.  Cutting the 50mm quilt with a sharp kitchen knife worked brilliantly, but we needed the knife sharpener on hand frequently.  Still a fiddly business.





It’s important to ensure the final fit of the two types is really good with no gaps or air pockets. Alex explained that it’s been so time consuming as all the rafter spacings are different because of the roof structure – the I-beams are sitting on top of the original existing rafters (this is one of the quirks of working on an old building put up, as Alex says “all over the place”, and dealing with materials produced for standard industry spacing on new builds).


Laying the insulation material as taken about a week in total, including putting the wind barrier membrane on the top, and they’re just finishing off the last bits of counter battening and the fascia boards. Then it’s all ready for the tilers to come in and finish off our lovely new super-insulated roof.
Our Thanks to Knauf for donating the airtightness membranes, tapes and roof insulation, all in German!

Next time?  Maybe use thicker 400mm I beams and pump with cellulose insulation: much quicker and easier than attempting to force the I beams to sit at regular spacings when the existing rafters were all over the place.

Cavity fill

We finally bit the bullet and agreed to pay the £2650 for the PUR cavity fill in an attempt to deal with the poor air test results.  Unfortunately the installer wanted us to drop the top scaffolding to give him access he wanted: But we can’t do that until the tiler has finished.  So were having to cover up the roof before we’ve run the next air test.  Not good.