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Going to insulate under floorboards tomorrow. Have about 6 brick courses underneath, and I've been down in the crawlspace. planning on using 200mm spaceblanket held up by mesh under the joists.

1. is there a problem with this - still be plenty of space for air movement.
2. in order to make sure the airbricks are clear, was planning on putting a 90 degree bend flat vent with a small section of trunking so it is down below the insulation to make sure they aren't blocked. good idea or not?

Thanks

By 200 spaceblanket I presume you mean some form of fibrous material, Jon. When you fit insulation you should make sure that there are no air gaps between the rolls of insulation or between the insulation and the structure that you are insulating. this means that you should have insulation between the floor joist and if more is required it is best to fix it at right angles to the previous layer to completely cover the joists and insulation.

I would advise using a sheet material fixed under the joists and with the long side at right angles to the joists and then use a fibrous material between the joists to fill the void completely. Before putting the floor boards back fix a draught proof membrane or boards, stirling board or hardboard, over the joists and tape all the joints between the boards or membrane and between the boards or membrane and the wall. This will prevent a major source of excess air change in the house. Draught proof the windows and doors as well.

Your idea for keeping the the air bricks clear is essential as well.

From my experience you will also need to ensure there is NO access for rodents. Mice love to live in, and make nests in rockwool at least, maybe also glass fibre.

woodburner wrote:From my experience you will also need to ensure there is NO access for rodents. Mice love to live in, and make nests in rockwool at least, maybe also glass fibre.

Already checked proofing - airbricks all intact and no access