Weeks 4 and 5: Looking up – work starts on the roof

Posted by on Apr 11, 2013 in Warm EnerPHit office | Comments Off on Weeks 4 and 5: Looking up – work starts on the roof

I’ve been away over the Easter holidays and on my first visit to the site since my return it’s clear that lots has been happening!

Creating a super-insulated roof

At the design stage Sally and Pete had much discussion over the best way to insulate the property’s roof.  The existing roof is high pitched and it has a extremely exposed location at the edge of Plymouth Sound.  The main concern in meeting the EnerPHit standard is achieving the required  airtightness of 1 ach@50Pa test pressure.   Normal loft insulation would mean that we would have had to have the airtightness layer on the ceiling below, which from an examination would not have worked as it was simply riddled with holes for electrics and cracks.  Because of this, it was decided to put a new insulation layer on top of the existing roof structure, with the airtightness layer on the inside.

Once the existing tiles were removed, OSB was used to provide the base to construct the airtight layer, across the whole roof. On site this proved to be an extremely challenging exercise – warping of the roof structure meant that it was particularly difficult to ensure the OSB could be laid flat without rebuilding the roof. It’s critical to ensure that everything goes right first time, as once the roof is finished it won’t be possible to get at the airtightness layer again to fix problems.roof I beams

The goal is to achieve an airtight, vapour tight layer above the OSB, with insulation above, and then a rain tight but vapour free layer above that. The airtightness membrane will go over the OSB, and then insulation of 300 mm is achieved by mounting timber I-beams above that. Mineral Fibre insulation will be snugly rolled out between the I-beams, providing the insulation layer.  I-beams are fantastic for this type of application as they have minimal timber bridging. This construction then needs to be sealed above with the final membrane layer  to ensure that no air is circulating in the insulation layer.

air,wind and insulation, the theory

The air and wind tight layers with insulation sandwiched between


The I-beams arrived this afternoon, greeted with a break in the clouds!

At this stage it’s still planned that the original tiles will be laid back on top afterwards, although of course some are damaged and will need replacing with new.

Airtight floors

Although the priority is to get the roof finished as soon as possible, with our wet winter weather showing no sign of letting up even this far into spring, progress is also being made inside.

Skirting boards are being installed, carefully ensuring that the airtight layer of the floor is sealed to the wall without being damaged. The airtight breather membrane, sandwiched between acoustic foam protective layers under the floor OSB, is glued to the wall. The skirting board is also then glued in place – straightforward but time consuming compared to the normal construction method of nailing. Each section also needs to be adequately supported whilst the glue dries to ensure that it stays in place.

Second airtightness test

Another airtightness test has been carried out this week, with a result of 6.4 ach. This is great news as our first airtightness test, which was done before work started, was above 30 ach, but there is still plenty to do if we are to achieve the less than 1 ach required for EnerPHit .