Single Storey Extension

Looking good, but on you're pitched roof insulation did you not need a vcb or need to tape up the joints?
Also I have to battern out for plaster board and not cut holes in the insulation for lights and cables.

I queried this with the Building Inspector but he said, it was fine and plasterboard could go up. Regarding the lights etc, again I followed his instruction, he has received plenty of photographs as we have gone along and he has been happy. The electrician asked that I did not cut the holes in the plasterboard as he wanted to do that himself.

Surely if you put in place a battened structure , you will have a void between the plasterboard and the first insulation? I thought that should be avoided but I might be wrong.
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Here is what my spec sheet says,

"Ceiling to be 12.5mm plasterboard with plaster skim coat on 25x50mm softwood battens on vapour control layer, Tyvek ref VCL SD2 or similar approved vapour control layer.

Important Note: Vapour control layer is not to be cut so as to accommodate any recessed light fittings. Should recessed light fittings be required, the size of the counter battens are to be increased as necessary.

Vapour control layer (vcl) to be installed as in accordance with manufacturer’s recommendations and specification.

Roof to be insulated with 2 layers of PIR insulation, 1 layer of 165mm Celotex insulation board reference XR165 placed tightly between the rafters and one layer of 20mm Celotex reference TB4020 in order to achieve a minimum ‘U’ value of 0.18 W/m2K.

Insulation to be installed as in accordance with manufacturer’s specification and recommendations.

Ventilation to the roof space will not be required, as roof covering is to incorporate a vapour-permeable breathable roofing membrane"

Batterning out is going to be a pain.
Interesting, maybe I have a cold roof and you have a warm one?

'A warm roof building will make the entire structure of the building warm in an attempt to avoid any cold bridging. It is where the insulation is located ‘above’ or ‘above and between’ timber rafters. Cold bridging refers to an element of the building (the roof in this case), which is allowing heat transfer and loss of energy. A cold pitched roof is where the insulation is placed either ‘between’ or ‘between and under’ the rafters or at ceiling joist level. This type of insulation system can be ventilated or not ventilated. However, if the roof is not ventilated then it will require a breathable membrane between the insulation and structure.'

Mine clearly is a cold roof. From the top down, I have tiles, breathable membrane, 50mm gap, 100mm insulation between joist, 40mm beneath joists. plasterboard.

I was told to have a 50mm gap between the membrane and the 100mm insulation to allow for condensation, but there should be no gap between the 40mm insulation and the plasterboard as the air gap here would allow condensation to form. You have been told to have a gap/void here so it is a bit confusing, unless we have differing roof types.
Must be the case, I guess different architects have different ideas on which roof system to use, or I wonder if it makes a difference on the type of flooring you use.

At least I know hopefully what kind of roof set I have now, the different options were nether mentioned to me when designing.
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Our drawings originally showed digging footings and a 'warm' roof. The Building Inspector thought this was 'over designing' and suggested building off a slab and having a more conventional 'cold' roof. So in short he suggested changes and I went with it because it was saving me a substantial amount of money.
I had to have a block and beam floor and go down 1.7 mtrs as we are clay here and had a couple of trees close by. I have down graded the insulation thickness which is still well in the allowed u value and saved me money, also going with Ecotherm insulation saved another £100. Will contact my architect and see what I definitely have but I think I also have a cold roof.
I have just had a look at your thread and your extension is not so different from mine. We have clay too, but there was a concrete parking area here for years, that we often parked small lorries or tractors on. So we poured another 8 inches of concrete on top with reinforcing mesh inserted. I think our building Inspector is an older person who is happy to apply some common sense. He was a builder before becoming a Building Inspector for the local authority, then moved to a private company.
Sounds like it, our inspector did seem a bit of a jobs worth, I removed one of the closer trees which was a large cooking apple tree which gave another meter before we hit the second tree which Is a walnut, thinking this would not mean such deep footing but he said no it would stay the same. He has moved areas and we now have a new person who I have yet to meet, hopefully he is a bit more relaxed.
Looking good, but on you're pitched roof insulation did you not need a vcb or need to tape up the joints?
Also I have to battern out for plaster board and not cut holes in the insulation for lights and cables.

its good practice not to cut downlights into through insulation as will can act as a chimley drawing warm air into cold space to condensate
plus tape joints for better job and vcb also batterns for service void okay
You guys had me worried, so I have been checking my emails to ensure that the photos I sent, was giving him (Building Controller) a very clear picture of what I have done with the insulation and the lighting.

The pictures are very clearly showing the insulation with 100mm square holes cut through it and cables hanging out.
He replied with,

'All looking good, it's ok to continue'

So I am happy that all is well, and I have the emails if there was to be a query later on.
Well, maybe he's happy with it but he won't be paying the gas bill or more importantly dealing with condensation in the roof - if it were to happen. It's up to you whether you want to follow best practices there, for extensions it's certainly less critical though. Make you're own mind up(y)
So is the roof a warm or cold? If it's a cold you don't want to cut down lighters in especially through the vcl.



Having a go at the tape and jointing, stopping in the screw heads etc. I think it may well turn out ok.
Looking good, I am also going too be taping the joints, watched loads of youtube videos :sneaky:, save the money on a complete plaster job, If it turns out bad then I will skim the whole thing. In other countries they lay there boards long ways so was unsure if I should leave the tapered edge on when it starts off from a corner or trip it off?

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