Loft Insulation....is there any reason why....

ic

I'd agree with the others here, just put a third layer of insulation on the loft floor above the rooms. I've done this with the npower offer - I now have something like 17 inches of insulation in the loft. The rockwool stuff they provide tears very easily, you'll have a mare of a time trying to attach it to the roof, even with netting.

Also, why hold the heat in the loft? It'll never get proper warm up there, you're just delaying the inevitable of that tiny bit of heat escaping the loft space, it won't really make a jot of difference to the temperature of the house below.

aliasojo

ic wrote: »

Also, why hold the heat in the loft? It'll never get proper warm up there, you're just delaying the inevitable of that tiny bit of heat escaping the loft space, it won't really make a jot of difference to the temperature of the house below.

I wasn't trying to heat the loft really, it was just to help cut down the risk of warm air from the house below rising and meeting cold air from outside the roof and therefore help minimise condensation.

David_Aldred

Hi - I have come across this with mineral quilt insulation laid over the trusses then roofing felt (non breathable) then tile battens and tiles in an early 1970's bungalow when folk were just starting to think about insulation. The one I inspected was wet on the cold side of the insulation where it was stuck as you say to the roofing felt and the condesnate was wetting the insulation and migrating into the rafters. In that case the situation was transient so there was no signifiant rot.

However if you start playing around with things such as making the insulation more effective it could become colder on the cold side of the insulation and more prone to condensation such that what was transient became sufficiently constant enough to commence decay. I guess what I am trying to say is the specification was never brilliant in the first place as you can see if you compare what was done in the 1970's with the current rockwool website diary and hence you may be better starting from scratch and altering to current methods if that is what you want otherwise I would leave it if there is no decay at present and just monitor things.

The insulation in the case I saw could be parted with time and care from the felt which is what that owner decided to do and left what insulation was left that was trapped directly between top of rafter and felt / batten. They then opted to insulate the ceilings / cross ventilated the roof void but that was their decision and it might not work for you.

Depending on the upgraded system you opt for you can still insulate at rafter level but just in a much better and efficient way less likley to produce condensate but bear in mind some systems you may well have to provide cross ventilation of the roof void to match specific new systems. Also have a look on the Kingspan website which is very imformative as well as Rockwool's - Kindest regards, David Aldred Independent damp and timber surveyor.

aliasojo

Thanks David, that was very helpful. This house is also of early 70's construction btw, and sounds very similar to your example. We also can feel wet between the insulation and felt sometimes which is why we thought extra insulation at that level would be more effective. Your comments make perfect sense though so I think we will concentrate on laying extra insulation at floor level and leave the roof level well alone.

David_Aldred

Hi - thanks for the kind comment - if you lay new insulation at ceiling level I would definately remove the insulation at rafter level because as indicated above the loft void above the new insulation will be colder and more prone to condensate as a result. Ensure cross ventilation of the roof void is adequate - all the best with this type of work which is messy and uncomfortable. Wear apropriate protection and put plenty of crawling boards down / have good safe lighting / plenty of sealed bags for disposal and somebody who is monitoring you up there. Kindest regards David Aldred Independent damp and timber surveyor