# Garden room project



## Humf (3 Jun 2022)

Hi all

I'm starting this thread to document my work on this new garden room build and hopefully get some pointers from far more experienced readers! A couple of times now I've asked questions on other threads, so thought it was time to start my own.

Disclaimer: this project will be very much DIY... I have no building quals and work in a completely unrelated profession so learning all the time. Plus, such as life, my time will be limited so this build is likely to evolve over quite a few months. Planning has already been months... if not years. 

*Aim*

Approx 2 years ago I built a small non-insulated shed as a trial run - 2.4m x 2.4m, apex felted roof, featherboard cladding - it went well. I used 4 equal sized framed panels, 16" centres and double top plates binding the wall panels together. I've created a very solid building that I now wish to replicate but on a larger scale. 

I'm not short of garden space, so the plan is to build a 9.6m x 3.6m wooden framed building, apex tiled roof and insulated. It will initially need to be a flexible space as we are having some substantial building work done on the main house and need a separate area to escape to when things get really disruptive. 

*Planning*

As far as planning goes, I've been in touch with the local planning dept. and they advise that permission will be required as we sit within Article 2(3) land and the building will sit over 20m from the main dwelling. This is actually not an entirely bad thing, as I now feel at liberty to design it to my desired size/height and make the most of the land available. There has also been a precedent set by several similar buildings in neighbouring gardens. A local arch' tech has offered to create the drawings and process the application. Although this comes at a cost, I'll be glad of his support and I will definitely need help with the roof design. 

*Work process*

I'm aiming to do as much of the work as possible myself but not yet ruled out the option of getting some help. e.g. there is already an armoured cable running to the site from the main house, as this provided the previous garden shed with power (installed by the previous owner with electricians certs provided). I'll use an electrician to complete all electrical work. I don't currently aim to have any other services running to/from the building, although I could easily be persuaded otherwise!

There are some tasks that I know will be a stetch e.g. roof tiling, doors and windows. So i can imagine drafting in help for certain parts of the build, if possible. 

*Plan*

First off - I'm not getting on well with SketchUp in the slightest! Can't fathom it whatsoever. I have many drawings on paper and will try to upload some once neat enough for public viewing. 

Onto the plan... because I lack any great skills or time (plus £ is always an important factor) I am keen to minimise cutting of sheet materials, timber and overall any waste. I notice Robin Clevett mentions the use of 450mm centres for framing, giving 3 equal cuts to 1200mm PIR i.e. 400mm panels of PIR with tape or foam to make up. 25mm each side being taken up by half a stud. He also mentions using 2700mm sheet materials (OSB) to accommodate 6 equal stud spacings. This sounds great in theory, but the 2700 OSB seems much more difficult to source and I'm reluctant to introduce any barriers that prevent obtaining good value timber. So taking this concept a little further, I realise 450mm goes into 3600mm equally by 8. So panels of 3.6m width seems a good solution. 

Whilst this takes care neatly of the PIR, there is then the issue of sheet materials being mainly sold imperial (2440 x 1220). However, I figured that if I go for 9mm external OSB sheeting, this is readily available in metric size of 2400 x 1200. I'm likely to use both an external and internal skin of OSB so the smaller thickness seems acceptable? Therefore a wall panel of 3600mm width and 2400mm height would be covered economically by 2 horizontal sheets and 1 vertical i.e. total width of panel = 2400 + 1200, total height of panel = 1200 + 1200 or 2400. 

All excellent... except... 3.6m x 2 gives a building of 7.2m - too small, 3.6m x 3 gives a building of 10.8m - just a fraction too big.

So my current plan is to use:

Long walls - 2 panels of 3.6m plus 1 panel of 2.4m 
Short walls - 1 panel of 3.6m
This gives a total footprint of 9.6m x 3.6m. 

I will keep to 450mm centres on the 2.4m panels and just reduce the final stud spacing to accommodate. 

My current thinking is to build studs using 4x2 timbers. I need help with roof design but would expect 6x2 rafters and ridge beam. 

*Groundworks and foundations*

The area is not easily accessible by vehicle, being quite some distance from the road. The site is on a gentle sloping gradient, falling on the shorter sides by approx. 400mm. 







The ground is very rocky with the area historically being quarried for limestone. I'm therefore not inclined to use a concrete base and instead use piers of some sort. Following on from some discussion on another thread about suitability of concrete blocks and appropriate depth of footings, I have since dug a couple of trial holes to investigate the ground conditions. The top layer is approx 15-20cm of softer stony ground and below that you hit rock (see first pic). Limestone being the way it is, the rocks are large pieces compressed together around smaller pieces and grit (see second pic) but there is another section of the garden where I've gone deep enough to hit pure limestone strata. 










Given the ground conditions, I don't believe a great depth of footing to be necessary. Instead I plan to excavate the top 200mm of softer ground and use hollow dense concrete blocks sat either on a bed of compacted MOT type 1 OR concrete. I'm thinking 2 blocks for the higher ground piers and 4 stacked blocks for the lower ground. These can potentially be filled with concrete and rebar driven through the hollows into the rock below. 

I have quite a few of these blocks left over from a retaining wall that was built (professionally) so it does make sense to put them to use. 

Using the general rule of footings being at least twice the width of the block, I propose digging these footings 880mm x 880mm, which would then accommodate two blocks side by side, measuring 440mm x 440mm. 

I have no idea how deep I'd get the rebar... the ground below the 200mm is seriously hard.. and I don't know how much use the rebar would be? I could also tie together the blocks together using some sort of metal ties, although I think the pre-cast grooves are on the shorter ends not width, so don't know how that would work.

*Next steps*

Most importantly, I need to get the plans drawn up and submitted to the planning dept. 

If I feel confident enough, in the meantime I'll put some hand drawn ones on here so anyone can tell me I'm way off track or doing ok. 

Block piers ... I'm seriously quite stuck on the spacing of these. I've looked at the span tables and if 6x2 C16 timber is used for bearers and floor joists at 450mm centres, then I think spans of 3006mm are permissible for buildings of less than 0.25kN/m2. However, I notice on Molynoox's build (which is a similar size of 9m x 3.7m) the groundscrew company were wanting spans of 1.5m but this was doubled up 4x2... my head is in a bit of a spin about how to go about designing this raft and piers... any help would be massively appreciated. I'm guessing some idea of the loading would be helpful! I'm very much hoping for fibre cement tiles which I know adds weight... 

*Final request* - please don't tell me to go out and buy a ready-made. I just can't stomach them and if this takes me many, many years, then so be it!


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## Jameshow (3 Jun 2022)

3m + .4 block with gives 3.4 X3 is over 9.6 so I would think that would be fine. 

Depending on what the loading on the floor is if heavy cast iron machinery you'll want double that and double layer of Plywood at which point your better off with a concrete floor.....


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## Humf (3 Jun 2022)

Ah yes... thanks. I'm forgetting that the span tables are written for 'clearance'. So I have to remember the double blocks (440mm) reduce this span.

Thinking about the block spacing across the shorter lengths, the side walls are 3.6m, so each of the floor joists will be 3.6 - 0.4 each end = 2.8, but I'm still thinking I'll be better with a centre bearer on blocks running the width of the 9.6m length. If that makes sense..? But how do I decide often to place these centre blocks? Obviously every joist can't be supported... oh hang on - I guess it's back to the span tables for calculating those too..

Also - I should have said - no heavy machinery or similar. The space will be mostly be additional living space (not sleeping) and my office. All lightweight really until my boys talk me into a pool table


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## Jameshow (3 Jun 2022)

How about making the floor a sip panel. 

I've just looked at our Scandinavian lodge expecting 8x2 framework and it's an 8x4 ring beam with a 6" deep sip on it. 10ft span....

Ply bottom insulation and ply top. 

Just a thought.


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## Molynoox (3 Jun 2022)

I think the quickest way to settle on a design is to show a sketch of your plans so people can see what you are proposing and can advise. I might be slow but I'm not clear what you plan is for your block pier spacing.
It isnt just groundscrew companies that advise 1.5m spacing, Im pretty sure it's the same with concrete piers and the like. In which case the span tables are mostly irrelevant because even a 4 X 2 will span over 2m which is more than the 1.5m. are you proposing spanning right over the 3m? It could be that the timber strength is not your constraint, if you plan on spanning over a full 3m or whatever then it puts all the stress onto the piers on the perimeter. That's cool if you have great foundations but it doesn't sound like you are all that confident in yours  might be better to hedge your bets and have more piers and thinner timber.

On SketchUp, if you did want to persevere then the SketchUp provided tutorials are excellent. I'm a visual learner and SketchUp was needed for me, but many others don't need it.

Martin


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## Humf (3 Jun 2022)

Hi Martin 

I’m not surprised you’re not clear… I’m not either! Agreed that some sketches posted on here will help so I’ll work on that asap.

No - I’m planning to support midway between the 3.6m lengths. It’s just a question of how many additional centre piers (at the 1.8m point) would be reasonable.


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## Humf (3 Jun 2022)

Jameshow said:


> How about making the floor a sip panel.
> 
> I've just looked at our Scandinavian lodge expecting 8x2 framework and it's an 8x4 ring beam with a 6" deep sip on it. 10ft span....
> 
> ...



Interesting thought. But I’m keen to keep everything simple. SIP panels are certainly appealing (I’m thinking rigidity and insulation value) but probably adds another complication for me to work out.


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## Jameshow (4 Jun 2022)

Humf said:


> Hi Martin
> 
> I’m not surprised you’re not clear… I’m not either! Agreed that some sketches posted on here will help so I’ll work on that asap.
> 
> No - I’m planning to support midway between the 3.6m lengths. It’s just a question of how many additional centre piers (at the 1.8m point) would be reasonable.


3??? 

But sips I meant ply insulation sandwich made up my you, much stiffer than an open joist floor...


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## Humf (4 Jun 2022)

Just sketched out a rough version of a design for the floor. I previously used 18mm ply (2440 x 1220) but as I’m trying my hardest to be resourceful, I can’t find a way to avoid cuts for this build. 

I like the look of 18mm T&G which comes in 2400 x 600 size and is readily available. The Egger board looks good as I’m certain there will be some weather resistance needed. This is why I went with ply on my previous build and it survived well until the building was water tight. 

The Egger board spec says supports upto 600mm joists, so this first layout makes use of that size centres. 

One thing I’m not sure about is how the intermediate joists are fixed, given that they are aligned and therefore entry from one side will be prevented. Is this a reason to double the central bearer?

Spans look to be good for the C16 6x2 I’m planning to use. The max span is 1960mm which is well within the 3006mm permissible span.

Piers/footings - I’m undecided whether (a) the type 1 should be replaced with concrete (b) sizing is appropriate. If I drive rebar through the rock below and up through the hollow blocks, then a concrete bed seems more suitable to keep the whole thing tied together. 

I had intended to sketch out an elevation (?) view of the pier & footing. Unfortunately ran out of space on this sheet. Will keep tidying up my rough sketches and post some more when I can.


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## Humf (4 Jun 2022)

Sorry the Egger T&G is 22mm


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## Humf (5 Jun 2022)

A flaw in the plan…

Just realised that although my 3.6m x 2.4m framework panels work perfectly for minimising cuts to studs, plates and PIR, the OSB sheathing would not land on studs centered at 450… arghh.


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## Jameshow (5 Jun 2022)

Centre your studs on 400 / 600mm???


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## Humf (5 Jun 2022)

Unless I’m missing something, none of the other options (400 / 600 / 16”) result in economical cuts to the PIR? Only the 450mm centres give you a nice 400mm space and therefore 3 equal cuts to a 1200mm piece of PIR…


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## Jameshow (5 Jun 2022)

But then your OSB dissent land on the studs? 

I'd go by OSB landing on studs and use any insulation offcuts under Windows etc?


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## Humf (5 Jun 2022)

Exactly.

Offcuts is an option as you say. 

Of course, 2700mm osb solves it nicely. Might make a few enquiries tomorrow.


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## Torx (5 Jun 2022)

One thing I’m doing with mine is drawing up the materials full size in simple 2D CAD to see ‘what fits what’. 

Having said that, I’m still expecting to lose money, but I’m not making sheds for a living and hopefully it’ll still end up cheaper than an off the shelf model (especially at my labour rate of £2.37/hr).


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## Humf (5 Jun 2022)

Sounds good Torx. What software are you using?


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## PDW125 (6 Jun 2022)

Humf said:


> Although this comes at a cost, I'll be glad of his support and I will definitely need help with the roof design.



your issue for planning doesn’t need an architect - they will be happy with a pencil sketch and location plan downloaded off one of the OS map providers. Your issue is size and you are in building regs territory over 30sqm so I would seriously consider reducing the size / length slightly which will mean you don’t need approvals on structure / insulation / etc. 

You could retain the total length as designed but add an open / covered area to one end so you would have an 8.4m internal space with a 1.2m open end - this wouldn’t need BRegs approval but would be just as useful. 

Also consider your roof design - a standard 22.5° apex roof will need around 8m of timber per truss profile, a 5° mono pitch will use half that. The apex roof will also require around 8-10% more covering, double the length of guttering and so on. 

If you want to get a lot of light into the shop but retain some security and wall space then also using a celestory or high level window would also benefit - using your panel design to create a rectangular box, you can then add on the top lights all along one edge which will increase light into the build but also mean you maximise wall space internally.


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## Humf (6 Jun 2022)

PDW125 said:


> your issue for planning doesn’t need an architect - they will be happy with a pencil sketch and location plan downloaded off one of the OS map providers. Your issue is size and you are in building regs territory over 30sqm so I would seriously consider reducing the size / length slightly which will mean you don’t need approvals on structure / insulation / etc.
> 
> You could retain the total length as designed but add an open / covered area to one end so you would have an 8.4m internal space with a 1.2m open end - this wouldn’t need BRegs approval but would be just as useful.
> 
> ...


Thank you for your reply - really appreciated and lots there to consider. 

The architect has been doing lots of work for us on a major renovation. So my chats with him have been very casual and tbh I'm half expecting him to look at my drawings (when eventually made!) and say they're fine to submit. But we'll see and your point taken. I see quite a few on the local planning portal that really are very basic pencil sketches, especially for annexes and garden rooms etc. 

Buillding regs - this is a really good suggestion and something I shouldn't have overlooked. I think when the council replied to my initial enquiry to say I'll need PP, I just thought sod it, and went about designing something the way I wanted. But I guess B regs are much better avoided. 

I like your idea of creating a veranda or similar covered area and had intended to do this anyway, reaching beyond the 9.6 x 3.6. I have the space to go further than the 1.2 but maybe a good option would be to keep the 1.2 covered and then have a raised terrace (decking) area which is not covered. That would offer the best of both worlds. I notice in terms of panel sizes, the new 8.4 lengths creates a 3.6m + 4.8m which is neat. Although I'm not sure I fancy lifting a 4.8 length frame into position ... the 2.4's on my previous build were chunky enough! Anyway, that's easy to sort. 

Pent vs apex is an interesting one... I'm not yet convinced either way. Apex I guess just has the aesthetic advantage imo, but I appreciate the savings on materials and workload with a pent. EPDM also seems more doable for an amateur such as myself. 

The celestory windows you mention... I'd been thinking of some 'letterbox' type along the rear wall. Your idea is similar but extended along the width of a wall? Sounds interesting....


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## PDW125 (6 Jun 2022)

@Humf glad of use - why not consider using 3.6m panels and one 1.2m with a door each side ..? That would give you your 8.4m and also if you made the doors opposite each other you would get boards / timber being able to be processed through the width of the building. 

If the architect is on-side then he will be of use - think about natural light and how you can use it rather than artificial light. And what I meant on celestory was just that - a row of letterbox windows on the top of your long back (or front..?) wall to let light in at high level. It also means your panels are all the same size / height and the windows give the lift.


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## Humf (14 Jun 2022)

I'm gradually finding my feet with SketchUp. Very early days so far and I'm sure there's things I'm not doing as quickly and accurately as possible e.g. the 'snap' function when joining timbers doesn't seem as intuitive as I'd like.

Just done the base so far, converting the hand drawn sketch above onto the app. Foundations next.


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## Humf (14 Jun 2022)

PDW125 said:


> your issue for planning doesn’t need an architect - they will be happy with a pencil sketch and location plan downloaded off one of the OS map providers. Your issue is size and you are in building regs territory over 30sqm so I would seriously consider reducing the size / length slightly which will mean you don’t need approvals on structure / insulation / etc.
> 
> You could retain the total length as designed but add an open / covered area to one end so you would have an 8.4m internal space with a 1.2m open end - this wouldn’t need BRegs approval but would be just as useful.
> 
> ...



I'm running with this idea and trying the building slightly shorter, at 8.4m x 3.6m. This leaves 1.2m of covered decking. I'm also planning to run the raised decking around the front too but not including this on the plans yet. 

Since the 1.2m will be covered by the roof, I'm including this within the base design, as the roof above will need proper support. The original layout of the concrete blocks was an even spacing but I've added an extra column of blocks sitting underneath the new corner at 1.2m. 

I'm not sure of the best layout tbh... (for info - I'm also going to develop this design with a pent roof)


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## PDW125 (15 Jun 2022)

For the sake of a few blocks, I think spanning 2.4m between piers is going to be pushing it especially with equipment etc loadings on the floor. I would go with 1.2m spans assuming these are single block on flat piers.


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## Humf (15 Jun 2022)

The blocks I have planned are the large high density hollow blocks. I have quite a few remaining from a professionally built retaining wall. They measure approx 440 x 220 x 220. My plan is to place two, side by side, and fill with rebar & concrete, driving the rebar down into the rocky ground below. I’d estimate I could achieve between 0.5/1m of depth for the rebar. 

The blocks will sit on a 880 x 880 size sub base of either type 1 or concrete, to a depth of approx 300mm. Not sure what’s best, compacted type 1 or concrete.

I’m reluctant to go as substantial for any intermediate blocks. Feels overkill. How about some standard 7.3N ones belly down, for the 1.2m supports in between my main piers? Is there any risk when mixing different size piers?


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## Humf (15 Jun 2022)

If I’ve got my calcs right, then the spans between piers are currently:

2400 - 220 - 220 = 1960

Which I think is ok for 6x2 at 600mm centres. But I take your point…


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## PDW125 (15 Jun 2022)

I’d just use them as they stand individually - won’t go anywhere if they are sat on a concrete pad and the rebar is probably only going to stop them moving sideways so 500mm tops will work.


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## Jameshow (16 Jun 2022)

I think you'll be perfectly fine. 

I cannot see it going anywhere.....


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## Humf (16 Jun 2022)

Thanks both. Currently working on a version that sticks with the main piers as shown (440 x 440) every 2.4m but adds single blocks (220 x 440) at the 1.2m points. Bit of a hybrid but I’ve got married to the idea of the main piers being 2 blocks!


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## morqthana (16 Jun 2022)

Some random points.

I've not used the latest version of Sketchup, so I can't be sure, but my prejudice says that an online tool accessed via a web browser (?) is going to be clunkier than a local app. There are sites which have archived old versions of free software - see if you can track down Sketchup Make 2017?

Remember that Building Regs threshold is internal floor area, not external building footprint. That said, obviously you want to avoid paying the oh-so-reasonable fees, but actually _complying _with the regs oughtn't to be a problem, unless you're building a ramshackle fally-down deathtrap of a shack. Which you're not.

Part P applies whatever though, but the electrician for the main work will be able to take care of that. Do you know what size the existing cable is? Better to be too big at first than too small in a few years time if your use changes and you need to trench a bigger one in.

Ditto other services, if they won't give planning a hissy fit (hint - don't tell them about water and drainage if you aren't proposing to use/connect them in this shed)

I don't know if Article 2(3) makes a difference, but if you build it so that it is _capable _of being moved as a complete structure (even if access realities mean you'd need a Sikorsky to do it) you may be able to avoid PP as it will count as a caravan.

And as for access - you can get micro diggers which are only 69cm wide.

Consider an ASHP for heating. (And cooling )


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## MikeJhn (17 Jun 2022)

Instead of blocks what I have used in the past is concrete fence posts, my office shed has been there for about twenty five years without moving and its on a slope.


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## Humf (20 Jun 2022)

Anyone seen these insulated panels before? I’m not really interested for the main structure but they sell them as roof panels only to be fixed onto timber frame buildings. Looks neat.


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## Humf (20 Jun 2022)

Thanks for your input Morq and Mike. Will reply properly when I’ve had chance to consider.


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## Mdhazell (24 Jun 2022)

Humf said:


> Anyone seen these insulated panels before? I’m not really interested for the main structure but they sell them as roof panels only to be fixed onto timber frame buildings. Looks neat.






Humf said:


> Anyone seen these insulated panels before? I’m not really interested for the main structure but they sell them as roof panels only to be fixed onto timber frame buildings. Looks neat.



They are an off shoot from Kingspan from what I can see. I've been looking at one of the buildings for my homebrew setup. Basically, it is Kingspan insulation sandwiched between 2 x 0.5mm sheets of treated steel. They reckon it is impossible for the steel to rust due to the process it goes through.
Hope this helps.
Mark


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## morqthana (24 Jun 2022)

Humf said:


>



I assume that counts as substantially non-combustible, given how close it is to the boundary. Talking of which, I don't know whose fence that is, but if it's his he'll regret not replacing it while he could still get at it.

As for speed - I recently had a 3m x 11m log cabin built in about 1½ days.


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