Garden Office - External stud wall on subfloor or joist ring?

[Dunksyo]

Hi all,

Long time lurker first time poster!

I’m currently in the research stage of my garden room/office. I’ll be going for a suspended floor on groundscrews, with a floor using double joists on the rim, then singles at 400 centres. All 6x2.

I’ve seen a few builds using Egger protect tongue and groove as the subfloor and then screwing/nailing the stud walls straight down on this but after reading through the Egger installation guides they recommend leaving a 10 mill expansion gap against any walls. Obviously this isn’t possible when the stud walls are fixed to the top of the Egger protect. Like so:

 

Or should I be mounting my stud sole plates onto the joists instead? And then laying the floor leaving a gap between the floor and sole the plate.

Is laying the subfloor to the end of the joists and then the stud walls on top acceptable from an expansion point of view? I’m looking at a floor size of around 6m by 3m.

Cheers,

[andyscotland]

Not quite the same, but my garden office is a SIPS build and certainly with those the OSB sheets that are sandwiched either side of the floor insulation run right to the outside edge and the walls sit on top.

 

My uniformed hunch is the expansion gap is important if the board terminates against a wall, to stop it pushing on the wall/bowing when the board expands. But less important if the wall sits on top, as in theory then the whole assembly can grow/slide slightly sideways.

 

As an aside, how will you be insulating your floor?

[saveasteading]

Sorry to say: that is a garden shed , and will be cold , damp and will rot.

 

I guess you've seen how groundscrews are hyped as the cheap and easy way for amateur construction. Yes they are, but for decking, fences etc I'd agree.

For a comfortable building you need damp proofing , materials that won't rot, insulation. Otherwise you will not be using it except as a store, until it falls apart in 10 years.

 

[Dunksyo]

1 hour ago, andyscotland said:

Not quite the same, but my garden office is a SIPS build and certainly with those the OSB sheets that are sandwiched either side of the floor insulation run right to the outside edge and the walls sit on top.

 

My uniformed hunch is the expansion gap is important if the board terminates against a wall, to stop it pushing on the wall/bowing when the board expands. But less important if the wall sits on top, as in theory then the whole assembly can grow/slide slightly sideways.

 

As an aside, how will you be insulating your floor?

 

That was my thinking re the lateral movement, if there's nothing to butt up against it won't need a space. For insulation it'll be 100mm PIR between the joists and subfloor. (warm roof with similar construction, and 90mm in the walls) I've not added it to my rough plan yet so I guess it looks like I'll be leaving it uninsulated which isn't the case!

 

28 minutes ago, saveasteading said:

Sorry to say: that is a garden shed , and will be cold , damp and will rot.

 

I guess you've seen how groundscrews are hyped as the cheap and easy way for amateur construction. Yes they are, but for decking, fences etc I'd agree.

For a comfortable building you need damp proofing , materials that won't rot, insulation. Otherwise you will not be using it except as a store, until it falls apart in 10 years.

 

 

Thanks for the reply! I've seen a few reputable tradesmen use groundcrews for similar builds, i.e https://www.youtube.com/watch?v=yueMxg8G948 and https://www.youtube.com/watch?v=vgcCMlRPkkk , they seem to be quite decent and well recommended. I am toying with the idea of a concrete insulated base but I'll need around 2.5m3 of concrete for the base which will probably need pumping from the front of the house to the end of the garden to stand laying it in time, so a bit unsure of the cost (imagine it's ££££) on that.

 

It will be insulated with 100mm PIR on the base below the subfloor, (warm roof with similar construction, and 90mm in the walls) the ground screws will raise it ~150mm from the ground and I'll probably look at putting some OSB + DPC on the bottom face of the base, but a bit unsure about the best way of doing that.

 

[saveasteading]

2 hours ago, Dunksyo said:

but a bit unsure about the best way of doing that.

Do a scale drawing and it will all become clearer. Nothing fancy and after some iteration you can put it up on here for comment.

I'm not always negative! Others may have done something like you are proposing.

But as a starter, how do you stop the deck from rotting? Tanalised timbers , maybe marine ply decking, then dpm, insulation and so on. 

 

2.5m3 of concrete is a morning of barrowing for 1 hefty labourer. So you are right that it is limiting.

A groundworker will do that, but for diy it's hard.

For diy I'd be inclined to site mix as it is takes the pressure off, and could be done in phases.

 

For cost comparison, what would be the screw pile cost?