Roof ventilation

[morfa]

I'm looking for some general DIY advice around roof ventilation.

When we moved into our current Victorial terrace, we had a gap in the roofspace through to our neighbour (we're an end terrace) and a condition of the mortgage was that this was blocked up. This really screwed with the ventilation in the roof and we had really bad condensation as a result. After a chat with our builder he suggested putting a few vent tiles on the roof. We did and it has improved things a bit, but not completely fixed them.

After a bit of looking around, I came across these plastic inserts which you can put in the membrane to improve ventilation:

http://www.aboutroofing.com/manthorpe-g ... lator.html

I installed 10 of them and it's made a slight improvement. But I've since done some more reading and apparently putting such things to make gaps in the membrane can be a really bad idea. So when looking for a solution to vent our bathroom fan externally, I came across this lapvent kit:

http://amzn.eu/fHp7cuM more details here - http://www.lapvent.co.uk/index.html

Would I be better off removing the plastic inserts and using a number of lapvents?

Can I use the lapvent to vent the bathroom fan (currently just vents into the loft, which isn't ideal...)?

Are the small plastic inserts ok? Or should I remove them all?

I'm happy to pay a roofer some money to come along and install a full set of soffit and ridge vents if that's what's needed. But if I can DIY (with the lapvents) then I'm quite happy to do that as well. Normally folk on here are excellent for advice, hence me asking.

 

[RobinBHM]

I would minimise the source of the moist air as a priority.

If you have a bathroom vent discharging into the roof space that will be loading the roof space with moist air -I would get this redirected through the roof

Do you have the loft well insulated at ceiling joist level? If you have insulation is it correctly detailed at the eaves? -if there is ventilation through soffits or cavity then these should still be able to circulate.

Does your water tank have a lid?

 

[morfa]

I have turned the bathroom fan off, so it's not pushing air out. But I'd imagine some is coming through.

No cold water tank.

Lots of insulation (which I put down) but I've left a decent gap at the edges as I'm aware that you need to ensure ventilation there.

 

[Woody2Shoes]

Hi - If it were me I would do everything possible to prevent warm, moisture-bearing air, rising (by convection or being blown!) into the roof space. I strongly suspect that ALL the damp problems are due to this. I would:

1) Urgently seek to re-direct all forced ventilation outside the building envelope (core-drilling a hole in the wall if necessary - there are a lot of traps for the unwary if you start interfering with roof coverings).

2) Think about air-tight sealing (e.g. with expanding foam, or foam strips) all penetrations through the ceiling (for wiring/pipework) and the loft door _ BUT - ensuring that there is proper eaves ventilation (not impeded by insulation) as well as at the ridge - so you can get proper cross-ventilation of the roof space.

3) Make sure that any water tank has no insulation under it and that all pipework is lagged (this serves two purposes - reducing/preventing condensation on the pipes as well as helping to avoid frost damage)

Cheers, W2S

 

[AndyT]

Re the bathroom fan - ours is a simple design that's easy for diy installation. A 100mm hole in the ceiling with a plastic insert and grille. Behind that a length of flexible hose to the fan, screwed to a joist, then another length of hose to a similar vent fixed in the eaves soffit. This outlet is not one big hole, it's a grid of 25mm holes, which means it was easy to drill from the outside, up a ladder.

No need for big core drill through the wall or a glazier to cut a hole in the window glass.

You definitely don't want that moist air venting into the loft. Something like I've described could be part of your improvements.