Smoke pellets for finding roof crawl space gaps

[mc2fool]

I live in a small self-managed 3-story purpose built (1978) block of flats, which has a mansard roof with the top flats in the roof, so to speak. It has a two communal stairwell windows, the top story one of which is a dormer and I recently noticed has a bit of a draft coming in from around the outside of the inside frame moulding.

I could, of course, just put some sealant around it but I was curious about the draft so I took off the moulding that side and prised open the side panel -- https://imgur.com/a/ymYFhzZ -- and whenever there's a breeze outside a veritable gale (well, almost ) blows through opening.

Just inside the brickwork there's a small gap, maybe 3 inches, that runs vertically and down into the crawl space between wall and roof, and is where the draft blows through from, and from there on to the window it's the cheek of the dormer and the outer frame, etc. The window itself looks well fitted and sealed outside. The crawl space isn't accessible. There's no obvious gaps or holes in the roof, soffits or anywhere else.

So, I'm wondering where the breeze is coming in, esp. with so much of it as a potential concern, and am thinking of getting some smoke pellets and using an old vacuum cleaner that has hose fittings on both in and out ends (and I already use, with bag removed, as a low power leaf blower) to suck in the smoke and blow it into the gap, and then watch from outside to see where it comes out.

Any thoughts on that?

For the pellets, maybe https://www.toolstation.com/shop/p38123 or https://www.diy.com/departments/rothenb ... 117_BQ.prd ? (Both shops being local to me).

[csearle]

I'm no expert but I recall that some spaces are often encouraged to be well ventilated, I imagine so that any build up of moisture is evaporated away. For example soffits (clearly not yours) often have circular vents in them.

Sorry can't contribute re the smoke pellets, I'll be interested in what others say.

Regards,
Chris

[PrincessB]

I recently noticed has a bit of a draft coming in from around the outside of the inside frame moulding.

Toolstation do a coloured smoke pellet which emits orange smoke that might be a bit easier to see from outside the building.

One more risky option could involve a smoke grenade (Easy enough to source from a Fireworks shop) - I'm going to leave this up to you regarding the safety of triggering a grenade inside the space to the left of the window and holding the panel shut while a lot of smoke fills the cavity.

Ignoring for a moment tha dangers of choking and burning the building down, the reaction from the grenade is heat based so the smoke will emerge under pressure which should force it through the airways within the structure to emerge from wherever the air is blowing in from.

Personally, I'd be inclined to seal the gap with some kind of removable sealant and check the seal was tight using smoke matches (also available from Toolstation) I'd also install a cheap humidistat in the stairwell and keep a bit of an eye on the readings just in case the airflow is masking some kind damp problem. The last thing you need is to fix an air leak and later on find you've got mould growing in the stairwell.

Regards,

B.

[mc2fool]

I'm no expert but I recall that some spaces are often encouraged to be well ventilated, I imagine so that any build up of moisture is evaporated away.

Possibly, although I suspect not in this case. The crawl space runs round the top floor, including the stairwell and flats, of which one is mine. When I got the place, some 15 years ago, I entered the crawl space around my flat (there's a cupboard under one of the windows and removing its side panel let's one get into the crawl space) and, while I didn't crawl round into the part by the stairwell, I remember shining a torch down it and seeing it did just continue that way.

Now, thing is, then (15 years ago) I spent quite a lot of time in the crawl space around my flat, putting in bookshelves and cupboards into it between the studs, and I don't remember any draughts then. Also, the insulation is on the outer side of the crawl space (i.e. between the rafters) so it wouldn't make much sense to have the crawl space itself well ventilated to the cold outside world. Unfortunately I can no longer access the stairwell part of the crawl space as a pair of those bookshelves now block the way.

Toolstation do a coloured smoke pellet which emits orange smoke that might be a bit easier to see from outside the building.

Yes, I'd spotted that but it says "orange dye may stain" and while that may not matter inside the crawl space I don't think the residents would be best pleased if some of the exterior tiles or soffits, etc, went orange.

As for a smoke grenade, yeah, pretty risky as I can't see how to without it coming into contact with timbers, and I think the residents would be even less best pleased if I burnt the place down!

[richlist]

When I have my chimney swept each year my sweep uses smoke pellets to check for leaks and airflow. These are readily available from wood burner stove suppliers and online. Perhaps you could use these.