Week 10 - Membranes, cellulose, zinc roof.
Entry posted by Benpointer in General
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A longer than usual blog - we’ve had a lot going on this week.
We definitely reached site capacity with five vans and seven contractors on-site on Thursday and Friday. Seven pallets of cellulose bales arriving mid-week didn’t help space management either.
The whole week got fairly stressful but somehow we seem to have got through it. Phew!
Membranes
The plan was for the team from SW Insulation to fit the VCL membrane to the vaulted ceilings, cross-batten with 25x50mm in preparation for the cellulose fill, then move on to the wall VCL and the additional 50mm PIR and 38mm service cavity battens on the walls. As I type that it sounds like rather a lot. It proved to be too much indeed…
Our lovely vaulted ceilings turned out to be a nightmare to fit membranes to. Those, plus the ceiling cross-battens (essential to stop the cellulose blowing the membranes off the rafters) took three guys pretty much all week to do. So the walls will have to be tackled when the team return on the 11th August.
We had no carpenters available Monday to Wednesday but on Thursday and Friday both Alan and Chris were on site. Chris rushed around closing all the external gaps around the roof edges off with OSB, while Alan worked flat out trying to keep ahead of the zinc roofers (see below). Closing off the roof edges was essential if we wanted to avoid the cellulose blowing into the rafter space and straight out across the neighbouring countryside.
Before:
After (ok, different section of roof but it all had to be done):
The pressure to prepare for the cellulose fill was heightened a bit because I’d cunningly agreed to the cellulose team coming in on Saturday to fill the roof…
Cellulose
Ray and Devlin from JW Insulating arrived mid-morning on Saturday and worked straight through to 6pm to fill all the rafter spaces. It wasn’t plain sailing - they were worried the membrane wouldn’t hold. They had to put a some extra edge battens in to make sure the membrane did not get blown off due to the pressure of the fill and they had a couple of ‘blow-outs’ they had to fix. Apologies for my terrible photography but here is Devlin blowing the cellulose in to one section:
After filling the first section they checked the density by cutting out a cylinder of the filled cellulose and weighing it. The core sample came out cleanly without disturbing the surrounding cellulose and after weighing they pushed it back in place and taped it up; it's amazing how the cellulose (which is simply pulped paper, treated to make it fire and mould resistant) seems to bind and 'set' in place once it is blown in. The test showed we were a tad over target density. I asked Ray whether that was a problem: “Not for you” was the reply. I assume they could end up using more cellulose than planned but they were happy to carry on.
By the end of the day we had a fully-filled roof. Another milestone achieved!
The photos don’t show it too clearly but the visual effect is as if there’s a vast silver duvet placed over the house. You can see the patches they used to cover up the entry points for the 'blowing hose'.
We hadn’t realised the cellulose blower was 3-phase and came with its own noisy diesel generator which ran for 9 hours non-stop. Not much fun for our neighbours - we’re hoping they forgive us. Fortunately it was all done in one day, so peace was restored today (Sunday).
Have we done the right thing?
Choosing the best approach for insulating the roof has been tricky. With hindsight, PIR between the rafters might have been easier (especially since I now know you can get open web rafters with PIR between the webs, so no voids to have to insulate).
Alternatively, maybe we’d have been better to have a warm roof with 200-250mm of PIR on top of the open web-rafters, which would then have served as service spaces for cables, pipes and MVHR ducting. That would have made for a very thick roof which would have been difficult to disguise though.
But we liked the idea of cellulose fill for its eco-credentials and its noise insulation levels (especially with a zinc roof). Having said that, to get to our target u-value (0.1 max) we still have to add another 100mm of PIR on the inside; we'll leave some channels to run the MVHR ducting through. That’s the next job for South West Insulating when they return on the 11th August.
Another option would have been to go for a more ‘Rolls-Royce’ solution like the timber frames offered by MBC, where they take responsibility for the roof insulation, VCL and airtightness. But although our costs for adding the insulation and membranes are higher than expected, it’s still going to be a lot cheaper than the MBC frame.
Anyway we* have made our decision so we have to stick with it and see it through; it’s definitely proving trickier to implement than anticipated though! (*Well me - I can’t blame Mrs P.)
Zinc roof
The zinc roofers, Wessex Metal Roofing were also working through the week, finishing the main roof, fitting the small areas of zinc facade, and various facias, ridges, and gutters trims. They also kept Alan busy on Thursday and Friday making sure the necessary ply backings were in place to keep ahead of them.
Scaffold issues:
One area of challenge we have is the scaffolding. Ideally we need some limited changes. The scaffold company are in a fix though - too much committed work for the people available. In fairness they are communicating well and being open about their issues: fitters unexpectedly leaving or having to be let go, holidays, potentially over-ambitious work commitments...
I have some sympathy but I sense it is going to be nigh on impossible to get them out for a minor adjustment any time soon. We’re going to need to think imaginatively to avoid being held up. I'm going to imagine everything's finished and we've moved in - feels better already.
Next week:
Work should start on the south-facing monoridge roof which is mainly solar PV panels with some slates round the edges. It’s a different roofing company because it seems the zinc roofers don’t do slates and vice versa. They sounded busy and stressed too, so I’m hoping they turn up.
Aside from that, it’s a quiet week. We were supposed to be doing the blown cellulose roof fill but.. oh.. I see that’s already been done!
Well done on getting to the end of that blog!
Just for fun I've added a summary 'dashboard' below. This is turning into a weekly project report - sorry about that: old habits.
Dashboard:
Contractor days on site this week: 26
Contractor days on site since build start: 156
Budget: Currently running £8k over (Benpointer budgeting rule 1 breached - poor management 😂).
Plan: On track to move in by Easter 2026.
Issues and worries closed this week:
- Making the roof space airtight enough for the cellulose blow.
- Completing the cellulose fill.
- Confirming the window and door opening sizes match the ordered windows and doors. (Actually that was checked as ok by the Norrsken pre-install visit last week but I forgot to mention it, but its a big tick in the box and would be a huge disappointment to C4 had we been on Grand Designs.)
Current top issues and worries:
- Scaffolding (see above).
- Velux flashings - more on this next week.
- Scheduling future deliveries: insulation, battening, cladding, render boards, MVHR, UFH kit, ASHP, HW cylinder, PV panels… all due in the next six weeks.
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