fixing gaps and splits in roofing felt in loft

[dave]

There are a few splits and some missing piece of roofing felt in our loft. The bitumen stuff I have for felt doesn't really work upside dow

- as I found to my cost! I have found some "liquid rubber" from the might B&Q and this claims to stick felt. It does. However it takes at least 12 hours to set. Standing in the loft holding a felt patch on for 12 hours does not appeal to me so I wonder if anyone has some clever way to hold the felt in place which the rubber adhesice cures? My thinking stops at wedging pieces of hardboard etc between the roof joists - but that doens't really work as only "hold" in one spot. Any ideas? Thanks

ps The felt in the loft is 40 years old. The above excepted, of looks in good condition. The new felts I see in B&Q etc seem a different type of thing. For starters the new stuff has "grains" which fall off all the time whereas the old stuff is dry and dust free and black - not "almost black". So - perhaps I am using the wrong type of felt? Your help would be appreciated.

[NT]

It sounds like you're referring to the layer under tiles or slates on a sloping roof. If so, this is a backup only, and its not normally necessary to repair it where broken. Plenty of roofs have no such lining.

NT

[Harry Bloomfield]

dave has brought this to us :

The stuff you found at B&Q is intended for hut roofs, roofs with no tiles on top. The felt you need is nothing like that. If it is only torn, just repair it with gaffa tape, making sure that any water which might get blown under the tiles would be channelled down onto the next level of felt.

[Dave Liquorice]

Yes, you want "sarking" and really needs to be inserted through the splits/tears such that any water running down the top of the old surface hits the top of the new and is carried down below the hole before being put back onto the top of the old. Bits stuck on will just catch the water and hold it there...

o o no no nHn on on on o o

o - old felt n - new felt H - Hole

Tuck the top end of the new behind a lath and the bottom end under a lath and you don't need any glue. It can be tricky near rafters and it might not be possible to produce a 100% leak proof section.

[gunsmith]

If its 40 years old and split the chances are its life expired and needs replacing. A non-trivial job.

[Kipper at sea]

The type of underlay felt you need is " type 1f =93, doubt if you will be able to get the bitumen stuff and its heavy but the newer underlay is light weight. Marley TX breather felt or a none breather 1f none bitumen stuff is ok. To hold it in place you can staple it to the back of the slate or tile lath. Down fall is that all the rolls of underlay felts come in 45 or 50 mtrs rolls, approx =A360 to =A3120 a roll.

[dave]

I think the phrase rhymes with "Clucking Bell" (c) Blackadder. Thanks all v.m.for the info.

[Jules]

Freecycle list, source some offcuts...

[John Rumm]

I suspect you are worrying about it a bit too much. The felt is there as a backup to prevent water ingress should a tile break or slip, and to catch any fine snow that blows up the roof slope and hence under the tiles. While routinely fitted on modern builds, it was not usually used on older properties. So the likelihood is your roof will continue to function just fine even with a split in the felt. The secondary problem is that to replace a section is difficult - you would really need to remove the tiles, and the battens, then refelt, batten and tile.

If you really want to patch it, then I would suggest an offcut of "torch on" underfelt and a hot air paint stripper. Wearing thick leather gloves, heat the end until it goes wet and glossy looking, and apply this at the end of the split. Press it down and hold it til it cools and sticks. Then fold the felt back so the underside is facing you. Now heat the edge of that, and then slide it along and press it into position - keep going to the end of the patch. The felt will "set" and achieve full bond strength in the space of time it takes to cool.

[dave]

Ah - ok - thanks!

[Dave Liquorice]

If the roof is in otherwise good condition, no slipped/missing tiles/slates then patching up the torn sarking is worth it if only to keep the powder snow out. I've taken half a dozen bucket fulls of powder snow from one of our roof spaces before now and it all came through a very small hole and it doesn't need to be a direct straight, as in you can see light, route from the outside to insdie for powder snow to find it's way in.

[Kipper at sea]

Don=92t even try to use heat in a confined space, even from a hot air gun, on old type 1f felt. The reinforcing webbing will act like a wick in a candle with the bitumen

[John Rumm]

Your concern being what exactly? Given you won't be getting it close to ignition temperature.

[Kipper at sea]

Just caution, hot air guns melt paint, I=92ve no idea what temperature they heat to. But I've seen them ignite dried grass in eaves that birds have used. You only need one strand to ignite in a loft. If bitumen isn=92t melted hot enough it won=92t stick. It as to be hot enough to soften the old felt to adhere.

[John Rumm]

They can get hot certainly (over 300 deg C, which would ignite paper)... Much depends on hte heat setting you use, and the amount of time you allow it to dwell on a surface.

However you only need reach about 150 deg C to start melting most SBS or APP felts.

Not really - as long as you melt the torch on felt, it tends to stick like STAB. You usually arrange it such that the surface you are heating is folled up or folded back on itself so that the substrate you are sticking it to is protected from the heat.

Obviously, I am not suggesting one does not need to take care - but if one is careful, the risks are fairly small and you get very fast and lasting results in a situation where applying patches via other means is difficult.