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Hi all

New member, I discovered this forum by accident looking for UK alternatives to Weber briquettes!

I have just recently had a large house extension done, and I thought it was sensible to do the back garden at the same time as it was cheaper to do whilst heavy equipment was on site.

I instructed the builders to build me a 7m x 3m concrete slab, with a single course of concrete blocks, they also left me a 100mm x 50mm wall floor plate concrete screwed to the blocks.

I have properly gone down the rabbit hole on this, and I am desperately trying to keep the budget under 2 grand as that is how much is in the kitty.

This is the area (with my Masterbuilt Gravity 560 for scale)


I had originally planned to do walls in 50x100 C24 treated on 600 centres, roof joists in 50x150 C24 treated again on 600 centres. I was going to sheath the roof in 18mm OSB and get a EPDM membrane to cover it. I was considering sheathing the outside of the walls in 11mm OSB and painting it, and put shiplap on the two small front walls.

To carry the roof load across the front opening, I was looking at a 6m beam in 50x250 C24 from a specialist supplier, but I am starting to think I may have massively over engineered this or I am missing a trick somewhere.

This sort of shows the layout I had envisaged originally.


The end game is one end as the BBQ area / outdoor kitchen, and the other end will be for seating, probably one of those L-shaped outdoor sofa things.

Any thoughts / ideas / criticisms / cunning plans will be exceedingly gratefully received!



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My post is not going to be constructive...however keep us updated on your progress please!

Maybe one day I can start a project similar to your own (pretty much the same, just rotated 90% anti-clockwise). Only thing I could suggest is to make sure the kitchen end has good natural ventilation to avoid any carbon monoxide build up if your going with charcoal bbq (surely the opening would be enough to eliminate any risk???)

Looks great already and looking forward to the finished result!😁👍

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I’m in the process of building a garden room and have been down many rabbit holes in the process. I’m virtually complete externally (just the epdm roof to fit) and then I can move onto the internal fit out. Sorry there’s not many answers below.

Firstly, take nothing below as gospel, and speak to your local building control officer as things can differ between local authorities. Sorry if I’m telling you how to suck eggs, it’s just a brain dump and may help others. With a £2k budget it would be a real shame to proceed down a certain route only to have to rectify or remove at a later date.

If budget is tight (it looks it 
️) consider most economical use of materials and the standard sizes these tend to come in. My build is 2.4m deep so just 1 standard sheet wide.  My roof joists came in 3.6m lengths, and were fitted as such.  I appreciate you’ve had a lovely baseplate already built so possibly a bit late.

Consult span tables for the correct joist sizing and spacing (link below). That said I’ve taken liberties with mine as it’s not a high traffic area and I’m not constrained by building control. It’s also a mini warm roof construction so pretty rigid. Have you considered an overhang around the building. You could leave say the top 200mm open for smoke to exit but the overhang would protect from the elements.

If building under permitted development, the structure needs to be 2.5m or less (take a look at the planning portal link below). Building regulations normally do not apply if under 15sqm. I ‘think’ an open structure like yours is considered an out build building.  Building control can confirm. Introducing building regs may lead you into having to build from ‘substantially non-combustible’ materials, such as blockwork, cement boards etc. due to your proximity to the neighbouring boundaries. If you look at the facebook group below and do a search on the subject you’ll see no single definition of non-combustible and what that means in practice.  Hence why I saw speak about your plans to your local BCO.

EPDM is a good system, but the rubber alone would swallow circa £600 of your budget. The OSB sheets would add another £300 nearly. Have you considered corrugated sheets?  
Access to the rear looks tight, so would you build a 7m wall in one? I built a 6m wall clad with osb then galv sheet it took 4 people to lift and position. Two of them had European powerlifting medals! I think you need a ‘fit and forget’ cladding, say metal sheeting or cement board. I’m not sure painted osb would give you longevity. Again, non-combustibility may be a factor (as noted above).

Oakwood Gardens Self Build Group on Facebook:
A great resource but not always helpful if you just want a ‘single’ voice. 


Ali Dymock
A DIYer who has been there (garden room build). I use this site when I don’t want 101 opinions from a Facebook group. Good info on framing and roofing.


Planning portal:

Span tables:



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@Toucs thats some great info, thank you very much.

I have had a brief chat with the building control people, they are quite happy as long as its under 2.5m max height, as its only semi-enclosed they don't seem worried about fire transmission as the only thing behind is more timber fencing then garden. They just seemed concerned that everything marries up with the published span tables and load is carried correctly.

Considering what you see garden outbuildings made of, I did chuckle at that lol.

After seeing someones galv steel roof, I am actively considering corrugated sheets, I have even started thinking about building the whole thing out of RHS or angle and welding it!

I could also put a support post in the middle of the open section, that might make it a lot easier, the concrete base is reinforced so it would take the point load OK.


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