Roof vents

[vicky whitworth]

You might remember that we have the most dreadful condensation in our roof because the eaves vents are blocked by insulation in the sloping ceilings in the bedrooms.

We have now found a builder who is going to sort out the problem plus do a couple of other jobs for us. He and I have been having a discussion about whether we should put in roof vents at ridge level at the same time as he's up there clearing the blocked eaves vents. We are roofed in double romans and he says that we might not need vents as the tiles - by their very design - are gappy. But my feeling is that we ought to put in something like lap vents while he's doing the job (belt and braces). We have non breathable felt under the tiles. Not listed.

Do you think we should have vents or will the tiles be gappy enough to let the air blow through at ridge level?

And if we need vents how many would you put in over a roof 10m long? Thank you.

 

[Flyfisher]

I may be misunderstanding this but if your roof is covered with non-breathable felt then I can't see how 'gappy' tiles can help the roofspace ventilation. Even removing the tiles altogether would still leave the roofspace sealed - wouldn't it?

 

[Feltwell]

I agree completely with FF. No tiles are airtight. What you need is ventilation through the impermeable felt. You'll get a bit of ventilation at the joints in the felt, but not enough that I'd be happy to leave it like that.

I'd introduce vent tiles of some kind, lapvent being the most unobtrusive I've seen.

 

[Penners]

if your roof is covered with non-breathable felt then I can't see how 'gappy' tiles can help the roofspace ventilation

I quite agree. However, if your 'felt' is a modern breathable one - Tyvek or some such - then it should permit breathing via the gappy tiles.

 

[chuckey]

Ever since a builder re-roofed my cottage using Tyvec, we have had a dampness problem in our newly decorated bedroom. Whenever I go into the loft it seems warm and humid so I bit the bullet, knocked out some stones and installed four air bricks (9" X 4") through the 24" thick gable end walls, knocked out a stone in to an unused flue and installed about 50 bits of 8" long 1/2" garden hose lengths. These were jammed into the overlaps of the tyvec so there is a proper air gap.
Only time will tell!!
Frank

 

[vicky whitworth]

Oh that's interesting. I had heard some doubts about breathable felt. We currently have non-breathable and I couldn't see how gappy tiles would help. The plan is to take about six rows of tiles off all round in order to access the voids that are stuffed with insulation. The builder then proposes replacing the breathable felt over the height of those six rows of tiles with breathable so we will have, in effect, the top half non breathable and the bottom half breathable. My understanding is that we need venting at the top and since that is in the non breathable bit we will need to put in vents.

Chuckey, how do the bits of garden hose help? Sounds cunning but I can't picture it.

 

[chuckey]

When the flags were off the roof and the battens removed, the first bit of"tyvec" was put on and stretched gable to gable at the bottom of the slope. The first battens were put on, then the second piece of "tyvec" was then put on overlapping the first, then more battens etc, etc. When I went up into the loft (Saturday!) and poked about, the overlaps with the "tyvec" were essentially airtight, visually the gap at the top of the overlap was less then 2mm, i.e. the two sheets were more or less touching. So stuffing two bits of garden hose down this crack then opened it up to about 14mm. While doing this I noticed that depending where the battens were, sometimes the material was actually tensioned against the underneath of the batten, so in this case there was no air gap at all. The roof is flagstones and was as drafty as can be, the trouble was that some stones were broken and needed replacing, also there was a problem with the line of the roof which was lifted by 4" along one slope.
Frank