Insulated timber-framed Garden Room

[Bodge it & Scarper]

Also... you'd probably get away some form of cheap thick polystyrene based insulation under the concrete, and then thinner more expensive rigid pir in the roof (celotex for example).

 

[Bagheera]

Wise words. How about 120mm insulation plus 100-105mm of screed to come up to level? Do I cut the DPM off from outside or should I fold it down or up? I am going to get a 300mm wide DPC and fold that up either side of the walls and put breather membrane over it so can I do the same with the DPM?

Also the DPM that goes under the concrete-where does that go at the edges?, does it wrap upwards around the sides of the concrete-I imagine water could get down the inside quite easily. The chap who's giving me advice from his project isn't using DPM below his concrete as apparently the rebar may pierce it-though I intend to keep my rebar a good few inches from any edge so can't see this being an issue. What do you think of that? He is having one below his screed of course though.

Also any thoughts on doubling the bottom or top plates? I've decided on 47mm x 100mm timber. The bottom plate (lower if x 2 will be treated-not sure about the rest)

So much to think about!

 

[Bodge it & Scarper]

Wise words. How about 120mm insulation plus 100-105mm of screed to come up to level? Do I cut the DPM off from outside or should I fold it down or up? I am going to get a 300mm wide DPC and fold that up either side of the walls and put breather membrane over it so can I do the same with the DPM? - personally I'd fold the Dpm outward over the top of the block, leave it flapping down the outside a few inches and then trim it off once I'd laid the dpm and sole plate. Folding the dpc up on the inside isn't a bad idea, I'd hesitate to do the same on the outside, there's sense in what your suggesting but if water does find itself down there the dpc could trap it like a gutter, you want any moisture to find its way out.

Also the DPM that goes under the concrete-where does that go at the edges?, does it wrap upwards around the sides of the concrete-I imagine water could get down the inside quite easily. The chap who's giving me advice from his project isn't using DPM below his concrete as apparently the rebar may pierce it-though I intend to keep my rebar a good few inches from any edge so can't see this being an issue. What do you think of that? He is having one below his screed of course though - you need to keep the rebar min 25mm off all edges and the bottom of the concrete, you can get concrete packers for this, commonly referred to as mars bars lol. If your closer then moisture could get to the rebar and blow the concrete, this is nicknamed concrete cancer. If you didn't have the dpm or were outside I'd want this to be more 50-75mm off the edges. Puncturing the dpm is a possibility with rebar, if you take care laying it you can minimise this. It can be patched up to an extent with duct tape and dpm, small holes patched up shouldn't give you too much to worry about. I'd be using a dpm personally.

Also any thoughts on doubling the bottom or top plates? I've decided on 47mm x 100mm timber. The bottom plate (lower if x 2 will be treated-not sure about the rest) - yea I'd double up, also allows you to lay a sole plate, then you can make stud panels with their own head and soul, lift them in place, your second head then binds all these together as well as help with to load of the roof. generally treated timbers only really stop insect attack, they won't do a lot for rot

So much to think about!- yea loads!!

 

[Bagheera]

Here's a pic of the site I promised. This is taken from the alleyway looking towards the house. I made the good decision to buy a breaker rather than rent as it is hot work and doing it for more than a couple of hours is exhausting. I went for the Screwfix Titan one at £150. I did try to buy second hand but one went on ebay for 100 so I thought hell, I'll but one and sell it at the end of the project. It's taking a long time as some of the concrete is really deep, but I'm getting there. I'm very much looking forward to going up rather than down but that's some way off yet....


I'm still pondering about foundations and the best way to do them but I have to get my planning in and I'm thinking about height today...

I want a warm roof structure I (dont want to faff with ventilation and want downlights so need room between rafters) but I also want a good ceiling height for a) storing ladders above my head and b) raising weights above head height if I turn it into a gym some day. I also thought I could be clever and get away with not having to cut all my 100x47x2400mm timber by keeping them at 2.4m. However I've ended up at around 3.2m which the planning officer made a sucking teeth noise when mentioned and it also may be rather imposing at the back of the garden. I have decreased the overhanging facia depth by not extending the rafters (only the firrings and above).

I could do a single top and bottom plate rather than doubling up but that would only reduce by 96mm (47x2).

here's a sketch, the interior floor to ceiling height should read 2575mm (47+47+2400+47+47-13(plasterboard)).



Any ideas if this will look fine/get past planning or if height can be reduced cleverly anywhere folks?? I'm 6ft btw so not super tall.

 

[Bodge it & Scarper]

Max height for a mono pitch roof on an outbuilding within permitted development is 3m, so you need to lose 262mm ideally 263 lol. I've forgotten how big the building is but, potential quick wins could include:

1. reduce height of walls so finish floor to finish ceiling is in the region of 2400, still ample room, downside being cutting all the studs down, although this need not take too long with a well set up chop saw and stop. IF you can find it you could get 4.5m timber and cut it in half? less waste.
2. consider removing the firing piece. You could achieve the fall using different height walls, for example 2.4 one side and 2.1 the other would give a fall (possibly more than you need, dependant on size and covering, EPDM can go as low as 1:80 I think). 2.1 is still enough room to stand up straight (unless your over 6'8) unless you really want a level ceiling.
3. again dependant on size of building but 220mm rafters seem slightly overkill, you could probably pinch a bit (20mm) here

doing those would get you under 3m. Also reconsider or get clever with the downlighters and you could leave the rafters exposed giving the feel of more height and useful storage space for ladders etc between the rafters.

you're doing the right thing with a warm deck, Imo always preferred to cold deck.

 

[victorgrey]

Just a quick update: I think I'll go for planning permission so I can put plumbing in from the start and may go higher than the 2.5m allowed under permitted development for the project i was planning.

In the meantime, a mini-project- I needed a new shed for garden equipment as I'm knocking down the existing garage so I got this done over the last month. It's made predominantly from scrap wood and sits to the side of the house. It rests on 6 flat bricks with pieces of pond liner on between to act as a DPM. The red cedar came from a neighbour. The pine cladding was £35 delivered from B and Q, pretty flimsy but did the job and it made the other door nice and light. Overall I think I spent about £70. The structure is from old roof rafters so it's a lot stronger than most commercial ones. Has two entrances, the end one for ease of getting the mower in and out. OSB roof with roofing felt. Should have brought the roof protruding over the sides but will fashion some trim to overhang.

View attachment 112391 View attachment 112392 View attachment 112399 View attachment 112394 View attachment 112395 View attachment 112396 View attachment 112397 View attachment 112398

I bought a wooden shed for a lot more than 70 bucks... damn it, haha, I love it but next time I should try to make it myself too.

 

[Bagheera]

@vitorgrey - yes, I'd highly recommend it, especially if you have a specific size in mind that isn't available. Also a lot sturdier than those bought even for the £400 mark

Bodge it & Scarper - it's not permitted development as it's right up to the boundary on one side but it will have a better chance of getting through planning if I do have it at no more than 3m.

All great suggestions!

Point 3- Having had a look at BuilderDepot.co.uk there are 47x200mm rafters available and as they are C24 I've had another look at the Trada span tables and I think you're right, I can use these at 400mm centres. I'll only being up there to tend my beehive if indeed I get one! 20mm saved.

Point 2-I was set on having a flat ceiling with downlighters but I've reconsidered on your suggestion and happy to get rid of the firring and instead have sloping rafters. Over 4.8m I'm going for a 1:60 now (required for a green roof should I do that at some point) which is only an 8 cm difference in height from one side to the other probably not too noticeable. 138mm saved.

Point 1- That brings it down to 3104mm. The ridge edge is only 20mm, not 30mm like I thought so now 3094mm. I've just bought a mitre saw from lidl, some would scoff but I've found their Parkside powertools to be pretty good in the past, so I can do that chop and stop. I'll take them down to 2300 (high side) so that's 100mm saved which comes to a grand total of 2994mm which leaves 6mm room for error/DPC/vapour membranes etc.

So internally I'll have double plates at top and bottom (47mm x 4) plus 2300mm stud = 2488mm height at the high side (2408mm at lower side) which brings me to your last point. I had planned for an OSB deck above the rafters but by replacing with boards or ply, it will look really clean. I'll paint the downward facing sides white before attaching and I think it will look really lovely and instead of downlights I'll go for some strip type so hopefully will look like this:



I could even run a V-groove router bit along the ply to give the appearance of boards (don't think it will weaken them significantly...?). All this, as you say, will mean that I don't need plasterboard so save 13mm in internal head height there and it gives the appearance of more space and I can store things between rafters if I want. I may resign my ladder to wall space however .

I'm yet to consider the overhang structure and I'm sure having the sloped rafters will present some issues with the walls but nothing I can't overcome I'm sure. Excellent stuff, thanks for your help!

BTW, I'm videoing everything as I go so will have it all on youtube at some point.

 

[Mattatooi]

Great thread. Looking forward to the videos!

 

[Bagheera]

Hello, it's been a while I know, I was away for a couple of weeks and it was too hot to do anything a couple of weeks back but the project is still alive and kicking. I did however have a big change of heart regarding the foundations. The expense, difficulty and coordination involved with concrete foundations was just a bit too much for me in the end, despite being sold on its benefits. Thanks to those who talked me through it, sorry I didn't go that way in the end! So I've changed to a floating floor on dense concrete blocks (7N). I guess one advantage is that when concrete cracks, you're a bit buggered but any subsidence with blocks can be sorted with a car jack and some extra hardcore.

Squaring the building was really tough as it turns out my garden isn't rectangular at all. I used a folding square, cross measurements and the 3,4,5 pythagorus (sp?) method to get it as square as possible.
I dug down to undisturbed hard earth and backfilled with hardcore that I had made whilst taking up the garage's concrete floor. Compacted this as I layered it up and some sharp sand on the top to level the first block off. I built up to the desired height and measured all 11 other piers off that first one, which was tricky yet satisfying when that bubble was sitting in the centre.

I purchased treated C16 5x2s (122x44/45) as maximum span between piers is no more than 2.2m (2x4s wouldn't have been strong enough). These were £9.80 inc VAT for a 4.8m length from a local timber merchant. I'm currently constructing the floor now. Where they're not supported by block piers I will use joist hangers. I'll be putting a weed control fabric on the floor underneath.

Here are some pics:









First video isn't too long away.

Does anyone know whether I should (or if it's desirable to) have a DPM between the blocks and the joists or not? Will a strip of DPC do?

Cheers!

 

[Bagheera]

 

[Joff-Turbo-Nova]

I see you have gone for the modular approach with the floor in 4 sections - much easier to manhandle around . Are you going to tie down the frame to the piers or leave free floating?

 

[Bagheera]

Yeh, I got a housmemate or two to help get them in position they just need screwing together and the whole thing squared. Not sure!-I'd like to attach them but no sure how the best way would be, suggestions?

 

[Joff-Turbo-Nova]

How about something along these lines to tie down the joists...

Joff

 

[Bagheera]

That could work, I'm a bit scared of splitting/cracking the blocks, though I suppose I do have spares. May go back and use construction adhesive between the blocks too.

 

[Bagheera]

Planning permission now granted! I can now go to 3m in height. Here are the drawings I submitted: