Hi everyone I’m planning to build a summer house this er summer and need info on sizes etc. The size of my plan is 2.5 m high 2.3 m deep and 7 m long plus a 2 m shed on the end of the summer house. For the corner posts 4”x4”? Floor and ceiling 2”x4”? This size is to reduce the step into the summer house. How far apart should the joists be? This will all sit on high density breeze blocks 4 in each hole, 3 rows by 8 rows. Where is a cheap place to get 4” thick insulation I’ve tried eBay about £400ish.
your joists need to be 16 inch centres using tannalised timber,
then a waterproof membrane over them then your floorboards.
as far as insulation, your best bet would go to a reputable builders merchant.