Summer house base and timber

[burts]

Sorry I wasn't clear.

If you put down the outer joists, then put a timber closing off the ends, that forms your base, then all this joists in between and screw in place - if they aren't sitting on a block they need joist hangers.

Then you can put your stud walls on top.

I did double joists at the end with a spacer, so there was something for the floor OSB sit sit on.

Ok, I’m with you now. So you mean build a frame and then joist in between it, fix floor deck then build up off it ( or walls up first then deck) Floating floor and not fixed down.
I’d have to have vents in the concrete blocks for this ?

I was talking screw sole plates for walls to outside of concrete block and then put joists on the inside of the concrete block. This way I thought the floor deck will be higher than sole plate for walls and Creates ventilation to outside via the breather membrane gap.

 

[Notch7]

Ok, I’m with you now. So you mean build a frame and then joist in between it, fix floor deck then build up off it ( or walls up first then deck) Floating floor and not fixed down.
I’d have to have vents in the concrete blocks for this ?

I was talking screw sole plates for walls to outside of concrete block and then put joists on the inside of the concrete block. This way I thought the floor deck will be higher than sole plate for walls and Creates ventilation to outside via the breather membrane gap.

You don't need concrete blocks all around perimeter.

You can just have them spaced apart.

You don't even need concrete blocks on top of a slab, just some plastic packers to raise off concrete. although the ventilation space is good practice

Ventilation via breather membrane isn't sufficient - it's pretty wind proof and would make the void rather pointless. The air gap you need is like the air bricks in a house.

If you want to fix structure down add some straps to bolt to slab

 

[Scarlet Pimpernel]

You don't need concrete blocks all around perimeter.

You can just have them spaced apart.

You don't even need concrete blocks on top of a slab, just some plastic packers to raise off concrete. although the ventilation space is good practice

Ventilation via breather membrane isn't sufficient - it's pretty wind proof and would make the void rather pointless. The air gap you need is like the air bricks in a house.

If you want to fix structure down add some straps to bolt to slab

I concur, that spaces in blocks will be adequate, but as a vermin protection would be needed, airbricks might as well be used.
These used vertical:

Or these.

I also concur that ventilation through the membrane would be insufficient for underfloor ventilation.

 

[burts]

I wanted to bring the cladding down to cover the blocks so it’s not unsightly. If I leave say 50mm at the bottom of the cladding and finish the breather membrane at the top of the blocks. Would that be ok?

So really I only needs blocks on the sides the joists will sit on? And could just close the other 2 sides off with a mesh to stop vermin.

What size joists will span 3m at 400mm centres?

Does the base need strapping down like a roof to blockwork?

 

[Captain Nemesis]

Durabase, groundscrews, adjustable pedestals.....

 

[burts]

Durabase, groundscrews, adjustable pedestals.....

Any links? The only durabase I know is tiling matting

 

[burts]

Durabase, groundscrews, adjustable pedestals.....

I didn’t even think about adjustable pedestals.... I saw the plastic strong enough to take the load of the walls and roof ‍
Have you done lots before?

 

[Scarlet Pimpernel]

I wanted to bring the cladding down to cover the blocks so it’s not unsightly. If I leave say 50mm at the bottom of the cladding and finish the breather membrane at the top of the blocks. Would that be ok?

Strictly speaking, you ought to have a membrane between the blocks and the timber. I would top the cladding at at least 150 mm above ground level.

So really I only needs blocks on the sides the joists will sit on? And could just close the other 2 sides off with a mesh to stop vermin.

What will the cladding for those two walls sit on? Will you bridge it with timber?

What size joists will span 3m at 400mm centres?

145 X 47mm

Does the base need strapping down like a roof to blockwork?

If your sole plate is fixed to your blocks, it may not be necessary, just belt and braces.

 

[burts]

I think I’m thinking far too much about it. The slab isn’t massively un level.

Can probably just space concrete blocks around the perimeter (not bedded, unless a levelling issue) maybe a couple through the centre. DPC between any block and timber, maybe doubled or tripled up to aid levelling.

Build a 145 x 47 frame, joists 400mm centres, 18mm OSB on top. Then build walls of the floor.
Maybe insulate between the joists, maybe not.

Shouldn’t go anywhere without being fixed unless there’s a tornado.

 

[Captain Nemesis]

Any links? The only durabase I know is tiling matting

https://durabase.co.uk/

 

[Captain Nemesis]

I didn’t even think about adjustable pedestals.... I saw the plastic strong enough to take the load of the walls and roof ‍
Have you done lots before?

Just suggesting systems I'm aware of. Adjustable pedestals for example will ensure accurate levelling and remove DPC concerns.

 

[Scarlet Pimpernel]

I think I’m thinking far too much about it. The slab isn’t massively un level.

Can probably just space concrete blocks around the perimeter (not bedded, unless a levelling issue) maybe a couple through the centre. DPC between any block and timber, maybe doubled or tripled up to aid levelling.

Build a 145 x 47 frame, joists 400mm centres, 18mm OSB on top. Then build walls of the floor.
Maybe insulate between the joists, maybe not.

Shouldn’t go anywhere without being fixed unless there’s a tornado.

I'd bed them. Any side wind could see the blocks being toppled.
And if the sole plate is not fixed to the blocks I'd use straps. Easy enough to use straight or twisted straps on the inside of the joists.

 

[burts]

I'd bed them. Any side wind could see the blocks being toppled.
And if the sole plate is not fixed to the blocks I'd use straps. Easy enough to use straight or twisted straps on the inside of the joists.

Toppled? They will be laying flat....

 

[burts]

Surely a concrete block laying down ain’t no getting blown anywhere ‍

Like Notch said, pointless having blocks the entire perimeter, and if I’m not doing that and the level isn’t massively an issue then surely it’s pointless bedding them down.

The sole plate will be screwed down through the OSB board. ‍

 

[Scarlet Pimpernel]

Toppled? They will be laying flat....

Ok, I forgot that, but movement by wind is still eminently possible if the blocks are connected to the cabin, and the blocks are not bedded.

Surely a concrete block laying down ain’t no getting blown anywhere

Don't underestimate the power of the wind.
One lone concrete block will not be moved by the wind because there is little area for the wind to act on it. But when you have a whole side of a cabin for the wind to act on, it's a whole new ballgame.

Like Notch said, pointless having blocks the entire perimeter, and if I’m not doing that and the level isn’t massively an issue then surely it’s pointless bedding them down.

The sole plate will be screwed down through the OSB board. ‍

I would still bed them down.
Will the sole plate, floor and/or joists be fixed to the blocks. I would have some form of fixing it to the blocks. If it's not it can be moved by the wind.