I'm DIYing my loft conversion (builder built the watertight structure and did roofwork, I'm doing all internals). It's hip to gable with a rear dormer.
Insulation wise, I have 90mm Celotex in between external studs. I am thinking whether or not I need to use 15mm OVER the studs too, or if it's overkill? Is it just to keep heat in, or is it to stop condensation from cold bridging on the studs? The roof is 120m between joists and rafters, with 25mm under, so definitely enough there. I'm also putting a vapour barrier (https://www.insulationshop.co/novia_1200g_vapour_control_layer.html?sp=1&search=novia) in the roof, but not the walls.
Bear in mind the house itself is only 3 years old with a lot of new build insulation as per regs, so already gets VERY hot in summer (almost unbearable in first floor bedrooms in summer).
If I'll be adding 15mm over the wall studs JUST to prevent heat loss, I don't see the point - in fact I'd rather the loft was cooler rather than hotter. As an example, before I put any roof insulation in, the loft was reaching almost 40 degrees last summer during the heatwave!
Building control (private) are fine with just 90mm between studs, but they seem quite relaxed on most matters so I thought I'd try and get a more technical answer here.
Insulation wise, I have 90mm Celotex in between external studs. I am thinking whether or not I need to use 15mm OVER the studs too, or if it's overkill? Is it just to keep heat in, or is it to stop condensation from cold bridging on the studs? The roof is 120m between joists and rafters, with 25mm under, so definitely enough there. I'm also putting a vapour barrier (https://www.insulationshop.co/novia_1200g_vapour_control_layer.html?sp=1&search=novia) in the roof, but not the walls.
Bear in mind the house itself is only 3 years old with a lot of new build insulation as per regs, so already gets VERY hot in summer (almost unbearable in first floor bedrooms in summer).
If I'll be adding 15mm over the wall studs JUST to prevent heat loss, I don't see the point - in fact I'd rather the loft was cooler rather than hotter. As an example, before I put any roof insulation in, the loft was reaching almost 40 degrees last summer during the heatwave!
Building control (private) are fine with just 90mm between studs, but they seem quite relaxed on most matters so I thought I'd try and get a more technical answer here.