Spray Foam Insulation

stickybookmark wrote: »

Can I ask what is a vapour check?

I'm aware of the 50mm ventilation requirement and have been told that it's hard to get it enforced as builders are inclined to push the insulation out to the felt unless you're standing there supervising them? I was advised to put board type insulation between the rafters to avoid that issue.
I haven't heard of the vapour check though

NIMAN wrote: »

Yeah the spray foam demo's I have seen on the net show a large piece of plastic being inserted between the rafters before the foam is applied, obviously to allow air to pass underneath?


Also, the loft space I am talking about is off two bedrooms, access gained through 2 doors in the wall. I think these 2 rooms are slightly colder than they should be, hence I am thinking it might be an idea to have a warm loft as the loft backs on to these rooms?

What about if I put down rockwool as usual, floor most of it, and then put this stuff across the rafters, would that foil make much difference?

cerastes wrote: »

If they require that, then dont employ anyone that would do that or that you cant trust to not do it, inspect the work yourself at the least.
What kind of target U-value is the OP looking for and why and what is the performance of sprayed foam?



Why not? what are you a fan of and why? working inwards, on the basis that PIR would want the joist and its own joints covered in an insulation layer and then covered in a vapour check layer and that layer barrier protected internally against damage, why wouldn't PIR be suitable?
It will have some of the highest thermal performance of insulation products per thickness, with additional layers to cover cold bridges and a vapour check layer how wouldnt this be suitable and if not
what is?

Im yet to be convinced of a spray foam insulation layer, although at least someone mentioned they put in a breathable layer that they spray up to, Id be concerned about completely embedding the joists in a non or very low breathable spray foam layer and certainly not up to the external/felt layer



Id be reasonably convinced the foil wrap is next to useless for thermal performance, I would not be convinced about foam filled insulation, Id have thought a mix of PIR and rockwool in different layers.

That plastic tray doesnt cover the full width between the joists, they look like they might be a good idea to stop insulation preventing an air gap being present but Id have thought only if they work across the full width of the gap? although a fabric external breathable layer fitted to create that gap and then filled with increasing densities of layers of insulation as you work inwards layered with a vapour check layer internally would offer insulation and protection from moisture escaping through the structure, how else is this vapour being handled then though?
That structure looks like its in the US, are any roof structures built that way here?

what is the performance of the insulation and what value is being tried to be achieved and why.

If there is one thing I'm concerned about is doing any work and for it to cost money but to not have any idea how well it will work or for someone to just throw up some insulation and say x or y R or U value is enough, ok but why? maybe they cant do the calculations or maybe they dont know or care about the potential risks.

stickybookmark wrote: »

what's your solution so for insulation between FF ceiling/attic floor joists when you intend putting plywood down over them to use the attic for storage?

If you don't approve of PIR in such situations (which is the application I mentioned using it in) and wool type insulation is going to get compressed by the plywood and not perform as well as it should, what would you recommend for attic floors?

nightster1 wrote: »

I wonder is this correct:-

The spray foam contractors who use Icynene say that the product is breathable therefore it can be sprayed directly onto the underside of felt and rafters. They say that water and air passes through the open cells in the product.

They also say that tile or slate vents can be installed in the attic to remove moist air to avoid the effects of condensation. Does anyone know if this is correct and is compliance with the Building Regs compromised?

thanks!

nightster1 wrote: »

this is a story and a half house built in 2007. Non breathable felt used.