Loft conversions are nice things to have but they often cost more per square metre of living space than an out-of-the-ground extension precisely because of head height issues and structural strengthening. And if you haven't got a garage or outbuildings you've lost a lot of storage space. They can be great spaces but you'll often pay a stiff price for it. Usually more to it than a while-you're-there job. The trouble with mineral wool insulation laid between the ceiling joists in the loft is that it leaves the void of the roof space cold. Insulation doesn't stop heat escaping, just slows it down. It'll get up there eventually and it'll be carrying masses of moisture from all the cooking, washing and breathing in the house below. Its a particularly bad combination with bitumen felt which doesn't breath and has no insulative value so it gets chilled. Warm moist air gathers in the roof space and condenses on the cold felt and moisture drips back down onto the mineral wool which rarely gets dry again except in high summer. The worst points are where the walls, roof slope and ceiling meet just below the wall plate and often this moisture shows up as a line of mildew along the junction of external walls and ceilings in top-floor rooms. Fitting PIR between the rafters means the loft space is the same climate as the rest of the house and the underside of the roof slope is warm so no condensation occurs. Its got to fitted correctly though. It mustn't fill the rafters right to their uppermost edge unless counter battening is used because an air gap of an inch or so needs to be maintained between insulation and sarking for ventilation and a gap should be left under the insulation at the wallplate and the ridge board so air can circulate and humidity can be vented. If you don't get the venting right with insulated rafters you'll have water running down the windows in the bedrooms. Its a fiddle but do it right and it transforms the house and once its done you can add extra mineral wool insulation without any risk of damp.
If you want long term effectiveness just rr-batten and felt mate easy enough. Im only in worcester if you wanted me to come and have a look so not too far! Message me if you need and ill take a ride over Cheers
You could also use trioso thermal roll over the rafters then over batten it a lot quicker and cheaper!
What depth of PIR is that equal to? Didn't think Superquilt provided as much insulation as 100 mm PIR. Probably better stuff now though.
super quilt what i used last was the same as 180mm of celotex. Haven't used it for a while and it changed a lot but was good stuff at the time!
Pity about that. Still, even a skylight (Velux, Fakro, or similar) in the roof would make the loft storage much more agreeable to use.
Very true. If you have a large plot with room for a ground extension, that would be a good option as you rightly say. But if the plot is tight for space (as city plots usually are), a loft conversion might be more feasible. Structural strengthening costs money of course, but it's also a good thing to do to a house anyway especially for older houses.
no,I cut roofs not tile em or diagnose problems! I have opinions but as birdie said, gimlet has pretty much covered it. It's the same as a vehicle, you have to weigh it up, how much do you throw at it as a stop gap before you finally bite the bullet? one thin I did pick up on was the head hight preventing a loft conversion, how high is the ceiling below? As in if its 10 foot you could lower it to 8 and fit ya lift conversion in....possibly...
Nail on the head with some of the problems I couldn't figure out (along with the leaky valleys). the wall/ceiling junction damp marks were puzzling me as I couldn't work out where they were coming from. right, lots of excellent answers, now to see what the various roofers/builders are looking to quote. thanks very much @Gimlet and all, very much appreciated. Pete
While you're figuring out what to do with the roof, make sure the mineral wool in the loft is kept back from the point where the ceiling and roof slope meet so that any moisture that runs down the underside of the felt can't come into contact with it. That will help in the meantime.
