Builder has not put in VCL in my flat roof, what can be done?

fanzhiyidan

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labcwarranty_Ventilated_Warm_Roof.jpg

Hi all,

 

I'm having a 4m x 5m garden office built at the moment (cavity wall construction).

 

My builder hasn't constructed my warm roof as per the detail I provided him (LABCwarranty.co.uk warm ventilated roof detail).

 

He hasn't completed the construction of the roof yet, is there any way of fixing it without having to strip off battens, insulation and the breather membrane he's put in the wrong place?

 

What he has done so far is (from underneath up):

• OSB3 deck.
• Breather membrane.
• Foil backed 100mm rigid insulation (joints are not taped).
• 1st layer of battens fixed through insulation into rafters.

 

There's 225mm x 50mm rafters underneath the OSB3 deck, could the VCL be installed here although I'll have spotlights and electrics running in this void.

 

The finish will be an EPDM membrane on top of the higher OSB3 layer.

BryanF

Put vapour barrier on side. You can buy spot light air-tightness covers. Use contega tape and primer @ wall and plaster over etc.

fanzhiyidan

https://www.boards.ie/discussion/comment/121317197#Comment_121317197

Thanks Bryan,

do you mean, put it on the inside?

I was thinking along those lines and was considering 2 options:

A: run the vapour barrier along the underneath of the joist, up the side of the joist, across the underside of the OSB, down the side of the next joist, under the joist etc. Then stick it to the block wall. I could notch the joists where required in advance for electrics. Then use a butyl tape on the underneath of the joists when installing the plasterboard.

B: add further insulation between the joists and underneath the OSB. Then install the VCL under the joists, up a bit of the sides of the joists to leave room for spotlights and services, across the underneath of the insulation, down the side of the next joist, etc. Again using butyl tape on the underneath of the joists when slabbing and sticking the VCL to the walls.

Is that what you're thinking, and if so, which one do you think might be better?

BryanF

B. you just run the vapour barrier straight through and use the back box type units for the spots.

BryanF

https://shopeu.partel.com/collections/accessories/products/airtight-downlight-cover

tbh if you have led spots with v little heat, I’m not sure I’d bother with back boxes

Mellor

What does of contract do you have with the builder? Was the construction documentation part of the contract?

If that's the case, maybe the builder remove insulation and install it correctly. FWIW, the detail in the OP is for a pitched zinc roof.

fanzhiyidan

https://www.boards.ie/discussion/comment/121323223#Comment_121323223

It's a friend of the family so no contract as such 🙄, just a sketch that he's not following at all.

I'm just trying to make sure there aren't going to be problems in the future.

Just been up on the roof now and he hasn't used treated battens either, it's turning out to be a bit of a mess.

In terms of the pitched zinc roof, would the method still be the same for an EPDM roof, allowing for ventilation under the EPDM deck?

Lumen

Not sure why there's so much focus on the inside, it's the outside that's the worst.

If I understand the current detail, if any water gets under the top deck it will pour straight through the untaped insulation joints, pool on the breather membrane, and then leak at the edges or through penetrations straight on to your electrics.

Take it up and do it properly. All the cutting is done, I can't imagine it'll take very long.

fanzhiyidan

https://www.boards.ie/discussion/comment/121326864#Comment_121326864

Yeah, I think I'll have to get him to take off the battens, tape the insulation and refit the battens.

How should he deal with the eaves detail in relation to the insulation/breather membrane and taping joints etc?

I'm going to do the VCL myself from the inside, at least I can take my time and get it right.

Should the battens be treated? Would it be ok to use Protim or Larsen wood preservative on the untreated battens instead?

10-10-20

The problem with option B is that you're going hybrid with that design and the risk is that any moisture which passes the VCL (it is a vapour control layer and not a vapour block) will become trapped between the foil on the insulation on the OSB and the insulation lower than it. Option A in my opinion might be best as it leaves the joists open and the VCL fully on the warm side.

Anyway, as long as the building isn't used for showering or cooking then the humidity load will be low so the risks lessen.

fanzhiyidan

https://www.boards.ie/discussion/comment/121331079#Comment_121331079

Thanks, it'll just be an office really. No showers/sink/toilet etc.

What are your thoughts on the untreated battens, is it ok to leave them or should they be replaced with treated timber or painted with preservative?

They'll be under OSB3 deck and EPDM finish. Vented front to back.

10-10-20

I don't think that they need treatment, they will be in a ventilated space and not expected to be exposed to rain. But I do see that they come treated and untreated. No harm in treating them, I suppose.

Have a look through Steve Roofer's videos, great tips there including using tissue faced insulation as opposed to foil.

https://www.youtube.com/watch?v=UKSaICT7wCE

https://www.youtube.com/watch?v=RthYYgzhMWU&t

fanzhiyidan

https://www.boards.ie/discussion/comment/121332634#Comment_121332634

Thanks, I'll take a look at them straight away!