Roof vents

[flash]

Hi,

I was busy painting my fascia/soffit boards at lunctime when some bloke wandered past and told me that my soffits had no vents in them and this was Not A Good Thing.

A quick lecture on roof ventilation and a wander round revealed the following.

No vents in any of the soffits. No gable end vents in the wall of the house. No vents in the roof or ridege.

My soffits are wooden so I was thinking of installing something like this:

my question is, will soffit vents be enough to create some airflow (the house does get very hot upstairs in summer) or do I need some roof/ridge vents as well.

Something like this

perhaps? Are thse easy to fit?

The house has a large roof with a pretty shallow pitch and concrete tiles.

Thanks in advance.

[Christian McArdle]

It depends on the construction of the roof. If you have breathable membrane sarking (or no sarking at all) and full fill insulation, then no additional roof ventilation is required.

Christian.

[flash]

Cheers. The house was built in the 1970s if that helps. If could you let me know how to identity the sarking, I'll have a look in the attic.

[Christian McArdle]

When standing in the loft what do you see looking up?

(a) Plasterboard (b) Hardboard (c) Insulation between rafters (d) Fabric above the rafters (e) Boarding above the rafters (f) The back of the tiles (g) Something else?

Also, is there insulation on the loft floor? Can you see daylight anywhere?

Christian.

[John Rumm]

First question would be do you need them?

How old is the property? Does it have sarking (i.e. under tile felt)? If it does, is it breathable?

Lots of older properties for example have no sarking at all and hence don't really need separate ventilation (enough air gets through the tiles).

Modern properties will often have a breathable sarking which again solves the problem.

Even many middle aged properties often have enough air gaps at the ends of the eves to cope.

You won't get much airflow as such (since it has not really got anywhere to flow). The main purpose of the ventilation is to preserve the roof timbers from rot by preventing a build up of moisture in them.

Cooling the roof space is a whole new ball game.

Yup, buy a hole saw to match, stick it on a drill, make a hole and push the plastic thing in.

[flash]

There is some sort of fabric above the rafters. It looks and feels like roofing felt (ie black and tarry). This goes all the way from the top to the bottom of the visible roof

There are rolls of insulation on the floor, with large blocks of polestyrene on top of some (but not all) of the insulation.

No sign of any daylight.

It is very hot!

[Christian McArdle]

OK, you have what was probably the most likely situation for a 1970s house. It is what is called a cold roof/cold loft with non breathable sarking. It's even called a cold loft in this weather! The term "cold" really means outside the house insulation zone.

It could certainly use some soffit ventilation.

Alternatively, if you want to climate control the space for storage reasons, perhaps with an eye for future conversion, you could take one of the following options:

Option 1: a) Install the soffit vents. b) Install kingspan between rafters, leaving 50mm ventilation gap between insulation and felt. c) Install further kingspan underneath rafters. d) Plasterboard over.

Option 2: a) Don't bother with soffit vents. b) Remove roof covering. c) Replace felt with breathable membrane d) Replace roof covering. e) Fully fill between rafters with kingspan f) Install further kingspan underneath rafters (less than in option 1) g) Plasterboard over

Option 2 is much more work, but provides a better solution. It is a good option if the roof covering is due for replacement anyway and you have an eye for future conversion. It provides, on average, about 5cm of extra headroom over option 1. Both options provide a "cold roof/warm loft" solution.

The ideal warm roof/warm loft situation requires more work and would raise the roof line by at least 5cm, usually requiring planning permission that would be refused on a semi or terraced house, although would provide additional head room.

Christian.

[flash]

Cheers for that. I can't see me doing anything with the loft space as it has a very low roof space (like less than six foot at the highest point).

If I fit the soffit vents do you think I also need some vents in the roof near the top? I ask because the stuff I've seen on the web has nifty diagrams showing cold air being sucked in the soffit vents and hot air being exhausted out of the top of the roof.

[Christian McArdle]

Ridge vents are ideal, but not necessary for an open loft with soffit ventilation, IMO.

Christian.

[flash]

Thanks. I'll put some soffit vents in for now and see how it goes.

[The Natural Philosopher]

Before you dop all that, wait for winter and go uypo there, and asess wherther or not te woodwork is in any way damp, and the space smells musty and airless.

Sofgfit vents make a roof into an icey place in winter, and reduce teh effect of the insulation due too sever draughts getting in.

Its your choice, but remember the requirements of a warm house and no rot in your beams are somewhat in opposition.

I am prtobablty ince teh BCO goes away going to plug up MOST of my soffit vents. The roof space is not so much ventilated as completely open to the elements - except rain.

ALL roof ventilation is about is making sure warm moist air from below doesn't get up and condense on your cold rafters.

If you have a vapour barrier underneath the insulation - and you bloody well should, IMHO - but not the BCO's text book, you do not need anything LIKE the ventalation they suggest.

I suspect their bventialtion requiremenst are a hangover from pre-vapour barrier days.

[Mike]

Totally agree on this. To my mind it should be in the regs yet new houses are still being built without it.

I've also had to meet the regs on the soffit ventilation and sometimes there's a gale blowing through. Does anybody know what the amount of air per second specified in the regs actually feels like ?