Spray Foam Insulation

The industry is worried about homeowners going to cowboy "removal" companies to get rid of the foam? What about all the cowboy installers of the foam?

It wasn't just sold as insulation but as a cheap way of glueing together a roof past its sell by date and in need of replacement. The ideal solution for nail rot and delaminating slates.

When I had my roof replaced (slate for tile) I had a conversation with my roofer. He indicated that he no longer would quote for a roof with foam - too much hassle. Unfortunately he had to take a few foamed slates off my neighbours adjoining roof to fit a hidden gutter to the back of the property. So, it may not just be the difficulty in selling but also a much more expensive roof replacement.

The current scam seems to be to attach a thin silver foil (as used by NASA) to the underside of the rafters. This wonder material is much better than other forms of insulation.

It's silly because a lot of new homes in the USA have spray foam insulation. They do enough of it to do it right.

I think the problem comes with not having a waterproof/airtight barrier between the loft and the outside - there they'd fit OSB sheathing and a vapour barrier over the whole roof surface which means the roof space is airtight, while here we just have tiles on battens and the roof is open to the outside.

We apply the spray foam to the underside of that 'wet' structure and it becomes wetter as it can't breathe, while in the US the structure is 'dry' and so spray foam is fine.

But you might have a good spray foam installation here everyone will scream bargepole. For example, the picture in the article looks ok to me. The timbers are exposed which means they're cold bridges, but also that they can breathe into the (warmer) loft space. So it seems to me that it's not a very good insulation installation to me (ie not worth doing IMHO), but it's not at risk of damp or rot. I'd need to check the condensation calculation to be sure, but at first glance there's no reason why that property should be unmortageable.

Theo

There are some installs where the cowboy didn't mix the chemicals properly, leading to noxious vapours in the house. But the install in the article doesn't look cowboy to me.

If you need a new roof you need a new roof. I don't think anything is going to change that. If the roof is wet and rotting, spray foam is likely to make that worse.

That's a problem with spray foam - it makes the roof a single unit. That makes it harder to patch it later. If you roof timbers were rotting, now you need to replace the lot.

Conduction, convection, radiation.

First fix convection. If there are any holes by which air is able to move out of an insulated space, plug them.

Single layer foil is great for radiation but not much good for conduction. Think 'space blanket' used by athletes - their body is radiating heat. Solar gain is mostly about radiation so it's good for blocking that. Spacecraft are all about radiation because there's no conduction in vacuum.

The better multifoils have a lot of layers to reduce conduction, but not as good as a sheet of PIR. However they're flexible so can be installed in places where PIR can't.

Theo

It's been used for years to hide rotten timbers and hold broken tiles/slates in place, and is also well known to cause rotten timbers even if they were OK to start with.

It basically knocks the cost of a complete replacement roof off the value of the house, because that's what you have to assume will be required.

My brother bought a 1920s house knowing it would need a new roof, tiles, battens, felt, but rafters were fine (it was not spray insulated). The adjoining property had spray foam insulation, and the roofer said to my brother the cost of reroofing that would be many times his roof. For a start, instead of a day to strip off all the old tiles and battens, it would take a week, and the rafters would all have to be replaced too. Also makes a massive mess which spreads over many gardens, and rather than just picking one day when you know it's not going to rain, you have to get the whole thing scaffolded with a temporary roof over the top.

The picture looks like something different to a roof. The article is about not being able to get a mortgage on a property where the roof has been foamed and hence the property is difficult to sell. In the USA roofs seem to be more like we use for cheap garden sheds, OBD sheeting covered in tarred felt material.

This is the picture, of a roof:

They may use 'shingles', but often there's a sheeting material behind. The shingles are a bit better than the thin felt we use on sheds, but won't last as long as cement tiles. They weigh less than tiles, which is important when the house is made of timber and not brick.

Theo

No, its important when the house is made of scrapyard rejects.

Timber frame and tiled roof is very common round here

In the USA what we use for shed roofing felt is called shingles but it doesn't necessarily come in rolls. It's cut in strips to imitate "traditional" wooden shingles.

This is a builder from Texas explaining how we do it wrong, in response to this story:

Really good - thanks for posting. Their 'code' insulation requirements are pretty impressive - well, certainly better than I thought they might be.

Yep - except humidity. I'd think mid-30% humidity is pretty rare in the UK. Inside, it's usually around 60% in my home - not sure how that relates to typical. Average outside humidity probably 70%+ most of the time. So if anything he's understating the problem where open cell foam is poorly installed.

There have been multiple kinds of felt over the years.

These smack of the "lazy way" of felt installs :-) There are better membrane materials to torch on a roof, than this. The membrane on my roof, is only two layers, vertically oriented and lapped. And the joints are quite resistant. If you do one horizontal and one vertical, the horizontal one can sag.

Shingles are generally reserved for a roof with a decent slope. If there is a danger of you falling off the roof because of traction issues, that's steep enough for shingles. Shingles come with "year ratings", like 10 year shingles or 15 year shingles. Usually, on a roof job, they could take a shovel, and just shovel the material off the sheath. Then they take nail guns and pallets of shingle tabs, and apply them in a lapped manner. The shingle will have a mineral particle applied to it for solar protection. Shingles are not particularly flexible, and will not remind you of a cloth in any way. There is some kind of substrate, and then a tar of some sort is applied.

Shingles can rip in a hurricane. The tabs on the shingle can curl, if the house is next to a tree. They don't hold up particularly well in a seaside application (that's more of a membrane job). And whatever the year rating is, you don't actually get that many years from it.

Tar paper might be considered a felt, because it's unlikely to be just paper. It might have some other sort of fiber in it. Tar paper is used on roofing jobs, it was used on house walls before applying a cladding to the outside, but it was replaced by Tyvek. Some country folk, apply tyvek (light light cloth) to the outside of their dwelling and then conveniently forget to apply a (more expensive) sheathing to the outside.

Here are some lads, putting Tyvek over a "chipboard palace". The intended application, is for sheathing to go on, within two weeks time.

Paul