Hello All,
I have just had my roof refurbished using the breathable white type 1F felt - this is, of course, layed on the rafters and battened down with the tiles put on the top. So far so good. But in this recent cold weather with the snow etc it seems that the inside of the white "felt" is getting condensation on it. Has anyone else noticed this?
Regards, Tom
maybe it's water vapour condensing before it can permeate through your breathable felt...?
JimK
Type 1F is not a breathable underlay. 1F is the ref to the old bitumen underlay. However there is a non-breathable felt on the market but the colour is black. In the case of breathable underlay "you get what you for" Some breathe better than others. You can pay as little as =A340 up to =A3100 per roll. Some of the underlays don=92t have a BBA cert. In my experience I=92ve seen cheap breather underlays sweat but not seen the better quality ones sweat.
How do you know if the underlay is breathable. Is it printed on the underlay.?
The only thing you can do to help combat the problem is fit ridge vents or vent tiles
if the membrane is not breathable how will venting the ridge and/or venting via some tiles (both *above* the underlay) help with the condensation seen on the *underside* (inner) of the underlay ?
JimK
The vents here poke through the felt. They are to ventilate the space under the felt.
JimK wibbled on Wednesday 23 December 2009 15:45
By allowing air to flow from the soffit vents under the membrane and out of the ridge vents. Both types of vent will require puncturing the membrane in order to do so.
Or am I missing something?
seems I may have been :>)) (never had a tiled roof)
Cheers JimK
I used non-breathable down the sides of a valley gutter when I rebuilt it. That was black. The back of it (facing into the loft) is slightly furry texture, which is intended to hold any condensation in place until it dries off, rather than let it accumulate into drips which can drip off or run down. Either it works very well, or there's never been any condensation up there (which seems unlikely, as some is inevitable; see thread on tin roofs).
On the back of a vent tile is a boxed section. Some have slots in to receive a pipe adaptor for use with a fan extractor or soil pipe The underlay is cut in a X and the four sides folded out wards and the vent tile is fitted in line with the opening in the underlay
To vent the ridge. The ridge tile and the tiles under it have to be removed also the underlay the length of the ridge tile as to be cut away between the top tile lath on both sides. If there is a ridge tree or board this can be cut out to give extra vent room. The tiles are re laid and the ridge vent tile re bedded in place. Vent tiles about 6ft or 2m apart, both sides of the roof fitted first course above ceiling height.
thanks JimK
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