Can I insulate over a timber garden room floor?

[jjohn]

I've had a garden room built but no insulation was installed under the floor. It's sitting on blocks but not high enough for me to install PIR underneath.

The floor is 20mm thick timber boards on 5 inch joists. Is there any type of thin insulation I could put above the floor before installing lino that would be effective?

Or could I spray foam the underside? Sorry if that's dumb I don't have a clue about this.

 

[noseall]

I've had a garden room built but no insulation was installed under the floor. It's sitting on blocks but not high enough for me to install PIR underneath.

The floor is 20mm thick timber boards on 5 inch joists. Is there any type of thin insulation I could put above the floor before installing lino that would be effective?

Or could I spray foam the underside? Sorry if that's dumb I don't have a clue about this.

Garden room? As in a shed type thing? Are the walls and roof insulated? Is the floor vented?

There is nothing stopping you fitting insulation between the joists. You could add a layer of insulation on top of the 20mm floor deck, but then you'd need another layer of ply to support your floor covering.

 

[jjohn]

Garden room? As in a shed type thing? Are the walls and roof insulated? Is the floor vented?

There is nothing stopping you fitting insulation between the joists. You could add a layer of insulation on top of the 20mm floor deck, but then you'd need another layer of ply to support your floor covering.

Yeah a shed more or less. I'm insulating the walls and roof myself but I can't get under the floor. The way it's built the walls are sitting on the floor. No it's not vented either should it be? The roof is vented with a 50mm gap above the insulation.

 

[noseall]

No it's not vented either should it be?

No, not especially. I was asking from a conventional build (non shed) point of view.

Do you have tolerance at the door threshold to add more material to the floor?

 

[jjohn]

Yeah I should do, I'll have to measure it later. Will I have problems with moisture under the floor if I just lay celotex down? Would 25mm even achieve much?

 

[noseall]

Will I have problems with moisture under the floor if I just lay celotex down?

No.

Would 25mm even achieve much?

It will be better than nothing. A lot depends on what you are asking from a glorified shed. How long do you propose spending in there, for instance...?

 

[jjohn]

I was hoping to use it as an office space, I probably should have done some more research before purchasing. Oh well, big coat it is.

Just so I'm clear here will I put batons down to what ever height of insulation I can fit in, celotex and tape, then screw plywood to batons? What thickness of ply would you recommend ?

Thanks

 

[robinbanks]

Got any pics of this shed and the flooring within? How much height do you have to play with? What will be the final floor covering?
Rigid board will bear any reasonable weight you might exert on it in an office context Personally I'd just lay the insulation, lay thin ply on it, perhaps glued down with something like LVT adhesive, then eg the laminate floor on that.

 

[noseall]

I was hoping to use it as an office space, I probably should have done some more research before purchasing. Oh well, big coat it is.

Just so I'm clear here will I put batons down to what ever height of insulation I can fit in, celotex and tape, then screw plywood to batons? What thickness of ply would you recommend ?

Thanks

You don't need battens.

Lay the insulation onto the existing deck (if you have the height tolerance), then fix ply or float glued together, T&G chipboard on top.

 

[noseall]

I was hoping to use it as an office space,

Then insulate the b'Jeezus out of it.

 

[robinbanks]

And consider an air to air heat pump that can cool it in summer

 

[jjohn]

Ok so I don't think I have the height to install any over floor insulation actually. There are 2 ceiling to floor windows with very little clearance from the floor to bottom of the pane. Here's some pictures:

And the door:

Here's pictures of the floor itself:

Is my only option here to lay some ecotec style 4mm roll to seal it for draughts then put the flooring down and hope for the beat? It's just going to be lino.

Could I get the underside of it sprayfoamed or is that just for internal insulation?

Re the heat pump/AC I was planning to put a mini split unit in it. The room in 4.6m x 3.4m and I was going to put in a 9000 BTU unit to try and avoid short cycling. Should I be oversizing the unit now?

 

[23vc]

Even 25mm (or 30, whatever you can get away with) PIR would be better than nothing. Guess you could possibly also insulate around the outside perimeter below the floor, with vents for the cross flow, using suitable insulation that can be in ground contact. Might take the edge off how cold the floor would get. Bit of a last resort tho

 

[23vc]

If whoever’s building these is doing them all like this, with upvc doors which suggests there’s a fair chance of them wanting to be used as a heated space, the floor design is a bit rubbish…

 

[jjohn]

If whoever’s building these is doing them all like this, with upvc doors which suggests there’s a fair chance of them wanting to be used as a heated space, the floor design is a bit rubbish…

Agreed. When I got the quote I told them I wanted the floor left open, they said no problem then built this. He said the floor doesn't really need insulated if you'd believe that.

Does 20mm celotex have a high enough compressive strength for the floor?

I only really have 30mm from floor to the window frame starts sloping in, doesn't leave much room for ply and finishing.