Where are my roof vents?

[floundering]

Hi.

I'm just in the process of putting in some insulation in a loft conversion, where we're doing the finishing off ourselves.

It's a tiled roof with old felt which isn't breathable, so we've had to have some vents put in, which were done by a roofer.

The vents on one side (west-facing) of the roof (both high and low vents) come right through the felt.

On the other side of the roof, there are only vents lower down and I can't see them at all from inside. Did they forget to make the holes in the felt on that side, or is there some good reason why the backs of those vents don't come through the felt? To be honest, I can't even tell where they are.

Should I search for the vents and cut the felt away myself so the air can circulate around from the 50mm air gap behind the insulation? Or should I just assume it's done right, stop worrying and get on with fitting the celotex?

Also, should I fret about the fact that between some rafters there are vents top and bottom but between quite a few of the other rafters there won't be any vents at all, top or bottom? Does this matter, or will the condensation find a way to travel around between rafters so it can get to the vents?

I don't want to be fussy about it but obviously I want to avoid condensation/damp problems later.

Many thanks for any help or enlightenment you can offer.

Cheers!

 

[floundering]

Um, so, okay, I have found the vents!

They are much lower than the floor level but can just about be seen by peering right down into the gap with the aid of a torch.

It's because it's a very old house and the front is not symmetrical with the back - so the roof itself continues down well beyond the floor level on one side.

I hadn't realised it was so extreme as there is no clue in the room below which hasn't got any pitched ceiling as you might expect. Quite a conundrum to see how it fits together, but at least I now know where the vents are!

So I can make sure the rockwool doesn't block the air flow from them.

There's quite a lot of breeze coming through them, too!

I'm still interested in hearing how the ventilation works in the gaps between rafters that have no vents. I suppose it's important that I leave enough space at the apex so there can be exchange along the whole ridge at that point?

 

[freddiemercurystwin]

I'm still interested in hearing how the ventilation works in the gaps between rafters that have no vents. I suppose it's important that I leave enough space at the apex so there can be exchange along the whole ridge at that point?

If you have felt (ie a non breathable membrane) then continuous ridge vents should be fitted or a tile vent at high level between each rafter. Otherwise the cavity between each rafter is only vented at the eaves.

 

[floundering]

I'm still interested in hearing how the ventilation works in the gaps between rafters that have no vents. I suppose it's important that I leave enough space at the apex so there can be exchange along the whole ridge at that point?

If you have felt (ie a non breathable membrane) then continuous ridge vents should be fitted or a tile vent at high level between each rafter. Otherwise the cavity between each rafter is only vented at the eaves.

Thanks for the reply.

Build control specified the number of individual vents, though. The roofers put in what was required by them and build control have looked at the work several times, so I don't know. What you say makes sense but I can't really afford (in time or money) to get more vents put in and I don't want to do more than build control think is necessary.

In some places we do have some breathable felt, because we had to have the roof mended in parts, so perhaps that made a difference. The breathable stuff is at the eaves on one side only.

I'll make sure there's a decent cavity above the insulation at the apex, all the way along. (Luckily this is possible, as there's a small strip of flat ceiling and I can cut the insulation so it doesn't fill more than it has to.)

That way presumably the air can circulate between rafters to some extent.

Is there anything else I can do to improve things, short of getting the roofer to put in more vents?

I've noticed that the horizontal overlaps between the pieces of old felt could be eased apart slightly. Since they're laid with the highest on the outside, and any water would run safely away on the outside, I'm tempted to loosen these a bit to create some minuscule air gaps. (Just so the layers are lying on top of each other rather than being sealed together. )

Is this insane or a good idea?

 

[freddiemercurystwin]

I've noticed that the horizontal overlaps between the pieces of old felt could be eased apart slightly. Since they're laid with the highest on the outside, and any water would run safely away on the outside, I'm tempted to loosen these a bit to create some minuscule air gaps. (Just so the layers are lying on top of each other rather than being sealed together. )

Is this insane?

No this is a well known bodge, you can shove some small timber wedges in the laps to keep the voids open.

 

[floundering]

Cool! Thanks for the tip.

 

[catlad]

You can get purpose made lap vents from a company called manthorpe or you can use wooden dolly pegs if you can still find them.

 

[floundering]

You can get purpose made lap vents from a company called manthorpe or you can use wooden dolly pegs if you can still find them.

Thanks - great tip.