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Hi everyone, first time posting here but I've been browsing the forums for a while whilst researching this project.
I'm building a garden room at the bottom of my garden. It will be used as a workshop and office.
I'm aiming to get get internal footprint as close to 30m2 as possible and as this will be right up to my boundary on 3 sides, to get it done within permitted development regs means it has to be made of "non-combustable" material.
Here's my current design for the top part of the build:
One of the main problems with a room like this is head height. In the above design I should end up with a floor-ceiling height of 2153mm providing I can get away with some of the choices I've made in the footings...
Roof
One of the main problems with the roof is the deep (4.8m, which is the longest joists I could find) span. Looking at span tables this means I have to use joists of 72x170mm with a 400mm spacing. On top of those will be firing strips for a 1/60 drop and then an 11mm OSB deck.
The'll be 100mm PIR insulation between joists (giving a 70mm air gap) and then plasterboard attached to the underside of the joists.
This seems like a very robust roof considering it's not supporting much weight and we don't have too much snowfall in London. Is this just how it has to be or does it seem overkill?
Lintels
To fit in a decent door height of 2020mm I've had to have just the wall plate sitting on the lintels with no bricks above. I think this should be ok but that seems like a lot of joists resting on a single 65mm concrete lintel over a 1800mm span.
Footings
This is where things might get a bit iffy...
I've tried to make the internal insulated concrete slab base the same level as ground level to maximise headroom. This means the DPC is only 50mm above both ground level and the inside floor.
I know this isn't ideal so to try and mitigate this I've avoided filling the soil right to the wall and added a channel of gravel. The idea is any water will run through this, off the foundation (which could be painted with a waterproof sealer) and in to the ground.
On the inside of the foundations there is a layer of hardcore, then sand to avoid the slab moving. Above that is 100mm insulation and then the 75mm slab with a reinforcement mesh.
There will a DPM from the DPC going under the slab and insulation.
Does all this sound sensible or is digging down like this a recipe for disaster?
Any feedback or pointers would be very welcome.
Am I overdoing things in places or under-doing them in others?
I'm building a garden room at the bottom of my garden. It will be used as a workshop and office.
I'm aiming to get get internal footprint as close to 30m2 as possible and as this will be right up to my boundary on 3 sides, to get it done within permitted development regs means it has to be made of "non-combustable" material.
Here's my current design for the top part of the build:
One of the main problems with a room like this is head height. In the above design I should end up with a floor-ceiling height of 2153mm providing I can get away with some of the choices I've made in the footings...
Roof
One of the main problems with the roof is the deep (4.8m, which is the longest joists I could find) span. Looking at span tables this means I have to use joists of 72x170mm with a 400mm spacing. On top of those will be firing strips for a 1/60 drop and then an 11mm OSB deck.
The'll be 100mm PIR insulation between joists (giving a 70mm air gap) and then plasterboard attached to the underside of the joists.
This seems like a very robust roof considering it's not supporting much weight and we don't have too much snowfall in London. Is this just how it has to be or does it seem overkill?
Lintels
To fit in a decent door height of 2020mm I've had to have just the wall plate sitting on the lintels with no bricks above. I think this should be ok but that seems like a lot of joists resting on a single 65mm concrete lintel over a 1800mm span.
Footings
This is where things might get a bit iffy...
I've tried to make the internal insulated concrete slab base the same level as ground level to maximise headroom. This means the DPC is only 50mm above both ground level and the inside floor.
I know this isn't ideal so to try and mitigate this I've avoided filling the soil right to the wall and added a channel of gravel. The idea is any water will run through this, off the foundation (which could be painted with a waterproof sealer) and in to the ground.
On the inside of the foundations there is a layer of hardcore, then sand to avoid the slab moving. Above that is 100mm insulation and then the 75mm slab with a reinforcement mesh.
There will a DPM from the DPC going under the slab and insulation.
Does all this sound sensible or is digging down like this a recipe for disaster?
Any feedback or pointers would be very welcome.
Am I overdoing things in places or under-doing them in others?
