My Garden Room Build - 9m x 4m

[user 36867]

Did you have to have planning permision

 

[Molynoox]

No, it isn't required for this build. The addition of a bathroom got me looking into building regs and building control, but in the end I avoided that too.
I did a post about planning permission earlier in this thread, there are more details there, but if you have some specific questions please just ask.
Martin

 

[Molynoox]

Mar 2022 - Screens, patio and lighting

Screens
I bought some screens from 'Charles and Ivy' and fixed them to the pergola, they are just what I was after so thumbs up for composite screens. Simply screwed in place, couldn't be easier.

Patio
I also made a patio / path.
Porcelain tiles from Tile Giant - happy with those too. I put down 100mm of MOT type 1, 50mm at a time and compacted manually with a tamper. Took me 2 weeks to do the foundations - could have been far quicker if I had hired a wacker plate. Sharp sand / cement mix, 5 to 1, on top of the MOT type 1, between 30 and 50mm thick. Slurry primer applied to the back of the porcelain tiles before laying them. I used a 1 in 40 fall for drainage, sloping away from the house. I also put in 150mm wide trench next to house, filled with small stones (Cotswold buff) because the height of the tiles was close to the '150mm above DPM' limit. I thought that would help prevent splash from rain.
I still need to grout the tiles.

Lighting
Added two more 'up and down' lights on the pergola, some festoon lighting from Amazon, and also pimped up the decking with LED strip pointing down at the ground. I used fully IP rated LED strip and installed them in a metal conduit with a diffuser panel over the top. Despite being quite a lot of effort, I'm not sure how I feel about the LED lighting. They do look spectacular, but there are two things that bother me a bit:
1. They are 'warm white' 3000k and yet they appear noticeably cooler than the wall lights. I'm not sure if this is because the wall lights are bouncing off the Cedar and making it look very orange, or because there is a genuine temp diff in the bulbs in both sets of lighting. Or a mixture of both.
2. The LED strip is very bright - once its completely dark they sort of overpower the other lighting a bit, and I'm not sure it does much for the 'ambience' if that's the right word.

So I'm not sure if the LED lighting is really needed, or if I should have just stuck with the up and down lights and the festoon lights,

Interested in other people's opinions on that one.

Last jobs remaining:

1. Grout the tiles
2. Topsoil to sort out the levels and grass seed.
3. Oil the Cedar cladding
4. Sort out the workshop interior with benches / cupboards etc

Martin

 

[Jameshow]

Is there anyway of hiding threads from the Mrs...!

 

[Marcusthehat]

Wow, mucho impressed!

 

[flying haggis]

very nice indeed

 

[Humf]

Hi Martin

Great read, thanks.

I’m currently planning a very similar build, although located in AONB and well over 50m from dwelling house so planning req’d.

One aspect I’m currently mulling over... the old chestnut of metric/imperial, sheet materials and reduced cutting/waste.

I noticed you went for 400mm spacing (not centres) on floor joists as this allows minimal cutting of PIR. However, you went with 400mm centres on wall studs? What was your thinking with this?

It seems to me that whatever you do, something ends up needing cuts. Hard to win either way.

For example, going with 450mm centres on wall studs, works well for PIR but leaves cuts for outer OSB.

Thanks in advance for any thoughts you have on this!

 

[Jameshow]

I'd go for 400 c2c pir is easier to cut.

 

[Humf]

Point taken. But pricier to waste?

 

[Adam W.]

That looks fabulous all lit up like that.

 

[Molynoox]

Hi Martin

Great read, thanks.

I’m currently planning a very similar build, although located in AONB and well over 50m from dwelling house so planning req’d.

One aspect I’m currently mulling over... the old chestnut of metric/imperial, sheet materials and reduced cutting/waste.

I noticed you went for 400mm spacing (not centres) on floor joists as this allows minimal cutting of PIR. However, you went with 400mm centres on wall studs? What was your thinking with this?

It seems to me that whatever you do, something ends up needing cuts. Hard to win either way.

For example, going with 450mm centres on wall studs, works well for PIR but leaves cuts for outer OSB.

Thanks in advance for any thoughts you have on this!

Hi
You are right about metric and imperial being a bit of a nightmare, however you can avoid it.
FLOOR
The floor isn't any issue regarding cutting the boards as you don't need the joins of the boards to land on a joist. So basically just maximise spacing for PIR on the floor and zero waste.
WALLS
with walls you would normally need to cut down imperial OSB sheets to be compatible with metric stud spacings, OR you would need to space the studs with Imperial but then you have the problem that plasterboard comes in metric sizes, and would need cutting
SOLUTION
My solution was originally to use 11mm OSB which DOES come in metric sizing
However, in the end I needed to use cement boards for sheathing, due to fireproof regulations, which comes in metric anyway. But 11mm OSB is the solution.

By the way, the roof is the same deal as the floor, metric spacings because the boards don't need to land on a roof joist.

Did that make sense?

Martin

 

[Molynoox]

That looks fabulous all lit up like that.

Thank you Adam
Martin

 

[Humf]

Yes makes sense thanks Martin.

Floor...

I’ve previously used 18mm ply for flooring (albeit on smaller non-insulated ‘practice’ sheds ) again sold in imperial. And I did line up the joins with joists.

I’m assuming the T&G boards don’t need joins fixing? If so, a good reason to use instead of ply. For my sheds, the ply was the final finished surface so better in that situation I think, resilience wise.

Roof... plasterboard would need to land on centres?

Walls... I notice Robin C mentions 11mm OSB is available in 2700mm lengths, divisible by 450mm into 6. This seems like a neat solution?

Excuse the slightly muddled thinking. I’ve had to put my sketches away because I was finding the question of centres and sheet materials utterly confusing. Then I discovered your thread. So thanks!

 

[Molynoox]

Yes makes sense thanks Martin.

Floor...

I’ve previously used 18mm ply for flooring (albeit on smaller non-insulated ‘practice’ sheds ) again sold in imperial. And I did line up the joins with joists.

I’m assuming the T&G boards don’t need joins fixing? If so, a good reason to use instead of ply. For my sheds, the ply was the final finished surface so better in that situation I think, resilience wise.

Roof... plasterboard would need to land on centres?

Walls... I notice Robin C mentions 11mm OSB is available in 2700mm lengths, divisible by 450mm into 6. This seems like a neat solution?

Excuse the slightly muddled thinking. I’ve had to put my sketches away because I was finding the question of centres and sheet materials utterly confusing. Then I discovered your thread. So thanks!

I'm really pleased the thread was useful for you, I put in quite a bit of detail, knowing how much effort I spent learning all that stuff and figured it might help somebody.

The T&G boards are PU glued together at the joins and also PU glued down onto the joists. They are also screwed down to the floor to stop them creaking. I reckon some people would advise landing the join on a joist, so make you own decision on that, but once its all glued together and screwed down its not going anywhere and I really don't think you need to land each join on a joist.

Roof... yes plasterboard needs to land on a joist. I think you can avoid doing that if you use super thick plasterboard (so it doesnt sag in the unsupported areas), but that is going to add cost and weight, and there is no need when you can just use metric spacings and avoid the hassle.

Yes I've seen RC using that 2700mm stuff, pretty neat if laying it down horizontal as it works out with nice spacings and no waste on the boards (width wise) if you use the 450 centres.
for a shed / garden room it might not work out any better than 'regular' metric board - depending what width that OSB comes in, I believe the 2700mm stuff is still 1200mm wide. my garden room internal walls are 2.05m at the back and 2.15 metres at the front - so the 2700mm would give no benefit on board utilisation as you would end up stacking two boards on top of one another to get the height, with same amount of waste as with a normal 2400 x 1200 board (a 1200mm board, in vertical orientation sits perfect across 4 studs @400 centres, but you need to cut the top for a 2.05m/2.15m wall)

I suppose the advantage of the 2700mm board is that the 450 centres could be nice for PIR utilisation because that gives a spacing of about 400mm. I think this is probably what you were thinking all along and I've just taken a little while to get there
However... if going 450 centres you couldn't use 2400 x 1200 plasterboard on inside... but I think you can get it in 1800 x 1200, so that could work if laid horizontally.... Without further thought I reckon that's the way to go unless I'm missing something - thanks for the idea

Martin

 

[Humf]

Yes that’s where I was going with it...!

Plasterboard is also available in 2700mm lengths so I think that’s why Robin says it works so well.

In terms of wall height, that’s a very good point about internal height and I’ll have to give it some thought. Externally though, since I’m having to apply for permission and also aiming for a pitched roof, I can (attempt) a design to suit materials to some extent. Two sheets of horizontal osb give 2.4m which will include double wall plate, stud, sole plate, plus some overhang to cover flooring and over floor frame, so not unreasonable without cutting I don’t think. Internal height needs some thought ... I guess it’s similar but minus the floor joist overlap & T&G thickness? (c. 100mm + 18mm = 120mm).

I noticed you had single wall plate? I’m thinking double because the corners tied up nicely last time and also I’m going to keep frames at a size that I can handle when lifting to upright position, so planning a series of panels rather than larger widths. I found 2.4m widths just about manageable last time. Tbh the more complex walls with kings & trimmers etc almost killed me ...! So the double plate will help me tie the smaller panels together.

cheers

 

[Molynoox]

Yes that’s where I was going with it...!

Plasterboard is also available in 2700mm lengths so I think that’s why Robin says it works so well.

In terms of wall height, that’s a very good point about internal height and I’ll have to give it some thought. Externally though, since I’m having to apply for permission and also aiming for a pitched roof, I can (attempt) a design to suit materials to some extent. Two sheets of horizontal osb give 2.4m which will include double wall plate, stud, sole plate, plus some overhang to cover flooring and over floor frame, so not unreasonable without cutting I don’t think. Internal height needs some thought ... I guess it’s similar but minus the floor joist overlap & T&G thickness? (c. 100mm + 18mm = 120mm).

I noticed you had single wall plate? I’m thinking double because the corners tied up nicely last time and also I’m going to keep frames at a size that I can handle when lifting to upright position, so planning a series of panels rather than larger widths. I found 2.4m widths just about manageable last time. Tbh the more complex walls with kings & trimmers etc almost killed me ...! So the double plate will help me tie the smaller panels together.

cheers

I think its a good idea to design your building around sheet materials in your case when you are not restricted to the 2.5m height of permitted development builds. Like you mention though, you still have the incompatibility / difference in height of the external OSB sheathing vs internal plasterboard, by the tune of about 120mm like you say (assuming you want the OSB to terminate exactly at the bottom of the joists - I would probably add another 30mm to help any drips keep away from the joists (assuming you have an air gap at bottom, which you may not, depending on your choice of foundations).

Here is a curveball option for you - put the OSB sheathing on the inside, that way it can be 2.4metres and 100% compatible with the plasterboard at 2.4m. It's actually technically better that way for condensate / moisture control too, although it probably doesn't feel like it if you listen to your instincts and look at what majority of builders do. Check out some of the shed building stickies - they talk about this option I think. Presumably you still have house wrap to cover up the PIR and studwork on the outside, and also the cladding / metal sheets.

For the wall plate (by the way I think the correct terminology is top plate for what you are refering to - wall plate is something slightly different). The reason I used only one is because that is all that is necessary if your studs are lined up with your roof joists which mine are as both use 400mm centres. I can understand the interest in using an offset between the first and second top plate to help connect things together - personally I prefer to connect the walls without that feature so I can tune it for plumb in situ without being restricted by the geometry of the top plate.

I also relate to your experience of lifting heavy walls - my biggest was a 5m length with a window and it was very close to my limit my walls are built using 5 x 2 also, so probably 25% heavier than most others - which I didn't really think about until I was lifting it....

you might want to do a build thread by the way.

Martin

 

[shed9]

The before and after view of that (going back to the start of the thread) is stunning.

Superb job.

 

[Molynoox]

thank you Shed9,. Considering our garden before (and for the last 15 years) neither my wife or I can believe it when we walk out into the garden sometimes "Is this really ours?"
Can't wait for the summer, I think it will be the first time we have had a garden we can sit in and feel relaxed instead of looking around and seeing things that need sorting out
Martin

 

[Humf]

Interesting. I had seen this in Mike’s design as well as others online. But like you say, hard to adjust when the majority of framing you see online places OSB on the exterior. I was probably thinking of doubling up and using osb on outside and inside of the frame. However, concern with that would be trapping moisture within the frame.

Ok - back to the drawing board with an internal wall height of 2.4m and just the breathable membrane, battens and wood cladding on outside.

I’m not yet sure about size of floor joists. We have incredibly rocky ground and the least amount of excavation the better for my wrists! I’m thinking concrete piers and the least possible, so it helps me to push spans and go for studier timber sizes eg. 6x2. I’m getting a local architectural tech to draw up my sketches so hoping he’ll assist. If not, we can get some structural calcs done. Anyway... my 100mm osb overlap was simply there to cover the join between bottom plate, floor sheets and joists. It doesn’t need to extend all the way to the bottom of joists, just enough to cover the above. I suppose with this new design (no external osb) it’s just a case of extending the breather membrane and battens below the bottom plate (sole).

Thanks for the correction on terminology... there does seem to be quite a bit of variation out there! I guess some of it is UK/US variations? Top and bottom makes sense to me anyway!!!

 

[Jameshow]

If using Pir tightly fitted then your unlikely to get condensation between OSB and insulation much like sips. Just DIY.....