insulating a refurbished slate roof

[afc26]

Hi,

I have recently a small extension at the rear of my terraced house slated over as it was previously covered with corrugated plastic. The felt and slates are up and now I need to insulate it.

I have no idea what to use. The area is approx 9 ft wide and 6 ft long with rafters every foot and a half. I'm aware that I need to leave a gap for ventilation as well. Could anyone help me and advise me what products is best?

I presume that after its insulated plaster boards are fixed to the rafters and its plastered to a good finish?

I am very appreciative of any help. Cheers Pete.

 

[noseall]

loft spaces are insulated against the ceiling and not against the rafters. a typical extension will have 100mm fibreglass between the ceiling joists with 150mm going across the joists.

a converted loft, whereby the space is being converted to habitable use, will have insulation fixed at the rafters.

this will either be a cool deck or a warm deck type of roof. either type should have been specified by your architect/designer, or at least mentioned by building control?

 

[afc26]

Thanks for reply!

Urm its not a loft but a ground floor extension that includes a downstairs toilet and a utility room.

Its very small only 9ft by 6 ft of a sloping roof that I have had slated over. I'm left with a roof on the inside where I can see the rafters and the waterproof lining of the slates. There is nothing else si I guess the gaps need to be filled and then boarded up.

I'm not sure what insulation to use.

 

[freddiemercurystwin]

It really depends how much you want to spend/how compliant with building regs you want it to be. Have a look at the PDF link below and refer to figure 4a on page 3 for how to install it. Kingspan is an excellent make and should be available at Jewsons or similar and for the amount you need shouldn't cost too much. Alternatively they may well do a 'budget' equivalent insulation but you'll probably need to use a thicker layer to achieve the same thermal resistance. If you wanted to achieve a building regulations compliant roof it would need to achieve a U value of 0.20W/m2K. If you go down the Kingspan route you'll need about 140mm Kingspan Kooltherm K7, if your rafters aren't that deep you'll need to plant some battens on the underside to give the extra space required. That 'U value' figure should mean something to blokey in Jewsons if you decide on a cheaper insulation and its that figure that determines how thick the insulation needs to be.
http://www.insulation.kingspan.com/uk/pdf/k7.pdf