Clueless Roof Insulator

[soundseleckta]

Hi,

I know ithere are many threads with regards to roof insulation but one thing i cant get the hang of is this moisture thing. I have a 1930s house with a slate roof, and no felt lining, aparently its the way it was done this. my loft space is drafty with lots of gaps at either end, i dont think there is ventilation at the eaves but there is some slots at the ridges. I bought plenty of insulation and plenty of celotex 50mm boards. I had a roofer come and see the loft and roof and said it was bone dry and just needed 3 slates replacing. as for insulation he said to put in kingspan. now the issues i have is about the gap between the insulation board and the slate (as i have no felt).. my joists are only 7.5 cm thick and the boards are 5cm thick which leaves 2.5cm haha... i read you need 5cm gap... i also read it only applies to roofs with felt and hence as i have not got any does that mean i can flush fit my boards or even fit with only 2.5 cm gap. im worried about ventilation as i am in the process of foaming any gaps at the sides of the roof where the brick foundations are. any tips?

 

[Blagard]

I have this feeling you are only telling us part of the picture.

Why are you insulating under the roof slopes. You should simply top up the insulation over the ceiling rafters and make sure your loft access is also nicely fitting and draft free.

You can use the loft for a bit of storage but that's all. Sure it will be drafty, cold in the winter hot in the summer, but dry.

Perhaps you could explain why you feel the need to insulate under the rafters?

 

[soundseleckta]

hi. thanks for the response. the story is that i want to make this house energy efficient. i was going to have all the slates removed just to put a felt lining in to make it water tight etc. initially we thought the joist where effected by water but the roofer discovered it was bone dry. he suggested leaving the felting as the slates and roof is in better condition than its age. hence to make energy efficient he suggested kingspan between the rafters to stop heat going out and topping up the current shabby insulation with new criss crossing to make it less peaceable to heat leak. from my research alot of folks are doing this to make a warm storage space. all i wanted to know is do i need to keep the air gap if 5cm in my unfelted roof and would moisture we a problem?

 

[WilliamEthen]

According to my knowledge loft insulation is an effective way to save energy and money at home.

 

[SurreyRoofingEstimator]

Basically you should be looking to stop heat elevating into the roof-space as much as you can (no point in heating an unused area) so proper insulation of the loft is the way to go, if it is possible to seal penetrations and such like into the loft all the better though that is nigh impossible.

Stick some rigid insulation to the loft hatch as well if poss to avoid a cold spot