I was going to leave my 600mm dwarf wall with an empty 50mm cavity, but now I'm considering fitting something like 25mm kingspan against the inside leaf. Is it worth it? Will this cause any problems?
If you have the floor insulated with 80mm kingspan, thermalite blocks, 28mm argon filled units to the frames and roof then it may be worth doing to save you £10 per year in heating bills.
If you just insulate the walls then you will only probably save about £1.00 per year
I'm putting 50mm kingspan under (and up the sides of) the slab and thermalite blocks on the inner skin. The windows and roof are 28mm and the frame is 70mm. I'm not sure about the gas - probably just air! It sounds like it's worth it then.
It will be a placebo. Because you know the wall is insulated you will 'feel' warmer, or think you are saving money on heating.
In reality most of the heat is going out through the roof - very quickly too if it is plastic.
If you are intent on insulating, then quilt in the cavity will be better as it will not only insulate from inside, but also from the outside, and will use the mass of the wall to regulate heat for summer and winter comfort.
Kingspan will just reflect radiant heat back into the room - some minor benefits in wintertime, but not what you want in the summer.
Would I need a full width DPC at the bottom then, to prevent the quilt touching the weak mix that's filling the cavity below DPC? (Currently I'm planning two separate 100m DPC's rather than one 250mm)
Would I need a full width DPC at the bottom then, to prevent the quilt touching the weak mix that's filling the cavity below DPC? (Currently I'm planning two separate 100m DPC's rather than one 250mm)
no absolutely not. in fact building control now ask us to fill the cavity void, with insulation below dpc too. the cavity fill insulation manufacturers insist their products do not wick the water up the insulation.
the gap between the cavities should not be breached unless you are setting up an oversite footing that is specced up for gas membrane. this is only required in areas vulnerable to gas seepage i.e. landfill sites, mine workings etc.
If you havent brought the glass roof units yet see if you have a local supplier of a solar control, gas filled, soft coat units. K2 (the roofing suppliers) have a trade named glass unit called celsius, others do a similar thing, check google
I have used this glass and can say its amazing! fitted in the summer on a very hot day, full sunshine and standing under the roof you felt no heat, bit like standing in the shade, expensive tho, expect to pay £100-200 a metre for the glass.
The roof I supplied and fitted was approx 4.5 x 3 and cost over 5k (Just the roof!)
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