[Closed] Loft ventilation bodge - awful or brilliant?

I really don't think an extractor is going to move that much heat from such an open space on a hot day. Will it make a difference? Yes. Will it make a noticeable difference? I doubt it. After all, given there is little ventilation right now, where is the fresh and cool air going to come from as you are pumping the hot air out?

You'd probably be better off putting a Velux in and opening it on a hot day - that would also give you working light and fresher air when you are up there.

You’d probably be better off putting a Velux in and opening it on a hot day – that would also give you working light and fresher air when you are up there.

That's what we have and it totally transforms the space. Loads of natural light and it has a vent you can open without opening the window. On hot days we open it up and open the loft hatch and it cools the whole house. Great for sweaty summer nights. Not cheap, but probably similar cost to getiing impoved eave ventilation.

Velux is likely to be £1000 fitted. Extractor fan would be up to £20 - £100.

Personally, I'd fit one in the end wall high up rather than try and duct back down - much better flow although you'd need to hire a scaffold tower for £100 and a core drill for another £100.

It'll move 250-330 cubic metres of hot air a hour, and draw in the same amount of much cooler air from outside through the airbricks.

The venting is insufficient to work passively, but it'll g=have no choice to let in air to replace what's being taken out by the fan. There'll still be some dead air spots, though.

Don't think velux is a good solution. I'd have to go up there on a hot day and open it, and remember to go back up there and close it again, and it's not a solution to the cost/time of getting roofers in. And because of the chimney stack in the middle of the roof space, wouldn't give working light to everywhere I'd need it.

Murray - no gables, hips all the way round

...although there are 3 flues in the chimbley stack and only one's being used...

Velux is likely to be £1000 fitted. Extractor fan would be up to £20 – £100.

But IMO it would be £1,000 invested rather than £100 wasted. We have the big loft-mounted inline Manrose fans in both our bathrooms (a smaller en-suite and a larger family bathroom). It works well in a small space but not as effectively in the larger room as it cannot shift the volume of warm moist air constantly generated and filling the larger space. It's fine when the shower is switched off though.

It’ll move 250-330 cubic metres of hot air a hour, and draw in the same amount of much cooler air from outside through the airbricks.

In your scenario you aren't simply shifting hot air trapped inside with cool air from outside - that replaced air is constantly being reheated as soon as it enters the space too.

FWIW, at our old place we had a loft room which got hot in the summer but opening the Velux was a very effective way of cooling it down.

That's my opinion anyway.

chimbley

Get out!

soz matt

In your scenario you aren’t simply shifting hot air trapped inside with cool air from outside – that replaced air is constantly being reheated as soon as it enters the space too.

FWIW, at our old place we had a loft room which got hot in the summer but opening the Velux was a very effective way of cooling it down.

Don't really understand how these are any different. Either way, you're letting air circulate - hot air out, cooler air in, rather than the air staying static and getting hotter and hotter.

I think the trickle effect from all areas is important IMO.

Are you going to keep the fan on constantly?

Don’t really understand how these are any different. Either way, you’re letting air circulate – hot air out, cooler air in, rather than the air staying static and getting hotter and hotter.

I don't think we are getting anywhere here - you asked if your idea was awful or brilliant and I gave my opinion but now you are trying to argue as to why it's actually brilliant so why don't you just crack on?

I'm just saying I don't think it will make much difference and that is my opinion. It will be interesting to see how you get on.

I have no view on whether forced ventilation is a good thing or not here, but I wouldn't connect it into the shower extractor vent. You risk blowing a portion of the dusty air back into the shower rather than out the vent. At the very least you need to make sure that there's a non-return flapper valve to prevent this, and even then I don't think I'd risk it.

sorry john, I'm not having a go, just trying to have a discussion and think through the pros and cons of different solutions. I'm inviting criticism of my idea because I don't know everything, but I'm also going to have a proper think about the criticism and see if it's valid and changes my mind. That's fair, isn't it? Thanks for your posts.

matt, either a temperature switch for hot days or a manual switch for working up there. Or both. I'm not an electrician, but there's the internet right here.

I totally agree constant, passive ventilation from continuous vents over a larger run of the eaves would be what you'd want if you were starting with a blank sheet of paper, but I haven't got one of those!

Cheers Phil, good point.

Okay, so you're going to be working up there. Velux, all the way (other brands are available and significantly cheaper).

My loft is as vented as it's probably possible to get without being leaky, our soffits let a lot of air through and it STILL gets as hot as the vindaloo shits up there in summer. When the skylight still opened it made a significant difference to the temperature in no time at all. That's the way I'd be going.

As for any nasties, get up there with a P3 respirator, proper rubber one rather than crappy disposables, strip everything back and vacuum everything. I did that and never had an issue since.

I'm guessing by your layout it's a 30s build with a huge loft space? If so that's well worth flinging a decent skylight into.

Soffit vents are easy to do as well, just watch for asbestos board.

When you say working up there, I assume you don't mean sat at a desk on a laptop?

Lap vents could be your solution - thin plastic devices that open up gaps between the layers of felt, so air can constantly flow across the roof space. Fit them in minutes, at staggered heights across both sides of roof so there's no dead air. The ones I ordered didn't actually fit between eaves, so I just bought a length of 15mm PVC pipe from Wickes for a fiver, cut into short (3 inch maybe?) sections, then opened up gaps in the felt that way. Just insert carefully so you don't rip felt. I fitted them to solve a really bad condensation issue in my loft (it worked a treat), so presumably the constant through-flow of air will help remove heat too.

no, dooosuk, only shifting stuff about and finishing the insulation.

Thanks squirrelking The upstairs rooms go up into the roof space, so it's not that big. It is 30's house though, you're dead right there!

Insulation job - I need to cut celotex to size and insulate the eves/skeilings. Except the joists are all spaced differently somewhere between 12" and 14", so they all need to be measured and cut individually.

And because the ceiling joists interfere with roof joists, I need to then cut each cut section in half, slide in one half down, shift it sideways underneath the end of the ceiling joist, then slide in the other half. All done on my belly, reaching down from the 45degree corner between roof and floor. Then when I've that another 40 odd times, then I can take the boards up, scoop up the vermiculite, bag it, hoover, fit loft legs, then insulate and re-board.

I did a third of it - one end of the loft to the chimney stack - 3 summers ago, haven't been able to muster the enthusiasm to do the rest!

cheers seabadger, I'll look into those too!

as per seabadger, in previous house fitted some of these and cured condensation issues

https://www.roofingsuperstore.co.uk/product/felt-lap-vent.html

I will also add a thumbs up for lap vents, cured condensation during the winter in my loft. Bought 40 off of Amazon and staggered them throughout the roof.

Why are you using celotex? Sounds incredibly slow, normally only used when its vital to maintain headroom by minimising insulation thickness. Also a bit pointless removing the old insulation, its still doing a job. Generally you would just lay extra insulation over the top at 90 degrees to the ceiling joists. The only insulation I removed was the stuff that had been stuffed between the rafters and joists, because you need to maintain an air gap (my outside soffets are below the ceiling joists so there is a 4" gap and then a big inaccessible void on all four sides of the house (mine is hips all round too). No point insulating down there as its not above a room, except one bay window ceiling.

Why are you using celotex?

There's some in the loft already, very odd job with a strip of the stuff running around the roof joists. Big gap below, above and behind.

Sounds incredibly slow,

Yes!

normally only used when its vital to maintain headroom by minimising insulation thickness

Exactly the case here. There's 10 or 12cm between the board of the skieling to the felt, and I need air to be able to move above the insulation. so 5cm celotex is perfect, apart from the incredibly slow process of fitting it.

Good point about removing the old vermiculite. I'm doing it because there's only about a 1" dusting of it, and I decided it would be good to give everything a proper clean before I fit the new insulation and board over. I'll have another think about that, though, ta.

Why don’t you go for a velux with a remote control that you can open from anywhere in the house? You can even get them with rain sensors so they close automatically during showers. Then you get light and air

That vermiculite, I was glad when I came across an empty bag in the loft stating it was asbestos free. Still used a mask as I had to move it around to treat the joists with woodworm killer. But more recently, I've seen a claim that it often was 'contaminated' with asbestos...so take care. I'm sure its fine as its beaded and doesn't seem to have any fibres sticking out of it or collecting under where it sits.

Does anyone know if early cavity wall insulation contained asbestos? It was injected through widely spaced 2" holes that were then dressed and stained to look like the bricks (practically impossible to see) and looks woolly. But there is quite a lot of overflow from the cavity into the soffits/loft.