Garden room patio door lintel?

[OxfordBlue26]

I’m at the early stages of planning a garden room self-build – I consider myself a competent DIYer, but have never attempted something on this scale, so hoping to get some advice here! The plan is for an 8m x 4m timber building (built on a contrete base), with an internal wall separating into a games room (5m x 4m), and office (3m x 4m). By the time wall thicknesses are taken into account, the internal floor space will be under 30m2 which should exempt us from building regs.

I’ve been watching lots of Youtube videos of garden room self builds and playing about with some preliminary designs for the structure (to try and get some approximate cost estimates!). I am planning on using 47 x 100mm timbers for the walls (at 400mm centres) with 47 x 200mm joists for the roof (a flat roof sloping front to back). Weighing up the pros and cons of cold versus warm roof construction, I think a warm roof would be the better option (the building will be more than 2 metres from any boundary, so we aren’t restricted to 2.5 metres height). Within the front wall, we are hoping to have sliding patio doors (not bifold) for the larger of the two rooms. My main question is about the required lintel for these patio doors. Hypothetically speaking, if we had 3 metre wide doors, would a wooden lintel constructed from two lengths of 47 x 200mm timber bolted together be adequate to support a warm roof? Or would a flitch steel be required (or something else?!)? If anyone could point me towards any website(s) that will help with the calculation on patio door width versus lintel construction that would be extremely helpful! Thanks in advance!

 

[tony1851]

Two 47 x 200 C24 screwed together would be fine - no need for a steel plate.

 

[Dereekoo]

As Tony, even with snow load of 75kg/m2 and roof load of 50kg/m2 you are well within accepted parameters for allowable bending moment and deflection (actual 4mm with snow, 2mm without)

 

[23vc]

I’d recommend definitely doing the warm roof. No venting/condensations worries.

 

[noseall]

Weighing up the pros and cons of cold versus warm roof construction,

As said - always warm!

 

[OxfordBlue26]

Thanks for the rapid responses everyone - that is perfect! I thought what I was suggesting would be fine, but thought it better to check!

I also had a quick question about height restrictions - as pointed out above, the building will be more than two metres from our neighbour's boundary, so as far as I can tell, we are allowed a maximum height of 3 metres without any form of planning/building regs. However, I was slightly confused about the 'maximum eves height' ruling of 2.5 metres. For a flat roof with a maximum height (at the front of the building) of let's say 2.8 metres, we would need a pretty aggressive slope to get under 2.5 metres high at the back of the building. I don't really understand why eves height should matter if the maximum height is within what's permitted? Or am I missing something here? To be honest, where I am planning to build, our garden room will be barely visible to our neighbours (their garden has some very dense trees/bushes at the boundary).

 

[23vc]

I thought the max eaves height 2.5 applies if you’re within a certain distance of the boundary, which you’re not?

And a roof going from 2.8m one end to 2.5m the other end is a max eaves height of 2.8m anyway…

 

[noseall]

Thanks for the rapid responses everyone - that is perfect! I thought what I was suggesting would be fine, but thought it better to check!

I also had a quick question about height restrictions - as pointed out above, the building will be more than two metres from our neighbour's boundary, so as far as I can tell, we are allowed a maximum height of 3 metres without any form of planning/building regs. However, I was slightly confused about the 'maximum eves height' ruling of 2.5 metres. For a flat roof with a maximum height (at the front of the building) of let's say 2.8 metres, we would need a pretty aggressive slope to get under 2.5 metres high at the back of the building. I don't really understand why eves height should matter if the maximum height is within what's permitted? Or am I missing something here? To be honest, where I am planning to build, our garden room will be barely visible to our neighbours (their garden has some very dense trees/bushes at the boundary).

2.5m max height above GL.