I was going to start a thread about a similar thing and then stumbled upon yours
@dlockers. I'm in the very early stages of convincing myself that I need to rip down my existing cabin and DIY a new one entirely. I have what I believe to be a Dunster cabin, or something of very similar construction. We inherited it when we moved in. It is solid 45mm tongue/groove stuff which slots one over the other. 4.5 x 2.5 ish metres. It's solid. Good roof. But it's seen better days and is rotten around the lower door frame and some of the floor. Sadly, the previous house owners that built it or had it built, decided to lay it on the bare garden (some shingle and mud). Inevitably, someone jumped through the floor earlier in the year after throwing a good darts score.
The problem with the Dunster style cabins are that each timber expands and contracts in the seasons and it moves. So you can't really take them seriously as structures as you can't attach anything to the internal "walls" as they move. So you can't really batten and insulate without the structure being at war with you. They are cabins to remain as summer houses/sheds really.
I want to pretty much build the cheapest replacement I can. I am limited in size as have a very small garden so needs to be similar to 4.5 x 2.5. I say cheap... I mean without scrimping on the important things like...ya know...it not rotting. Solid and well insulated. Also needs to be within 2.5m total height as right up to boundary. I only really want a door and a single small window as it's primary function is a home office and storage as we have no garage (converted to bedroom).
I've watched countless videos on the matter and to get going, I've been debating the two main factors which will account for all the plans. The base and the roof construction. I'm definitely going to build all 4 walls the same height, then use firrings to raise the front side to keep it as simple/quick as possible.
The earlier Oakwood Garden Rooms / Garden Room Guru videos are good.
Some questions...
Where do you buy giant tarps and how much are they? My main concern with these projects is that we live in the UK where it rains daily. The chipboard floor you used I would have been worried about that swelling up. In fact I see a lot of people use OSB for the floor or even ply in case of water issues. What made you chose the tongue and groove chipboard? Cost? I feel like I'd be constantly rushing to not have things get wet and have nowhere to store stuff whilst it will be in progress.
Giant tarps? I got the door covering one years ago from Amazon when my kitchen roof sprang a leak. I can't remember cost. For this one being so large I ordered a damp proof course/visqueen for 38 quid as a temporary cover.
Chipboard is quite forgiving if it gets wet. Get p5 and it'll retain it's integrity if it gets wet, but it must dry out. If you are definitely going to be leaving it outside and uncovered during wet, then egger protect do a 'waterproof' version with a cover. I'm not sure why people use OSB tbh.
In terms of the base, mine will be small and the ground is already very flat. I like the idea of the screw/rods method you used, but I just feel like it's a faff compared to just pouring a concrete pad? What's the cost difference? I see more people doing raised timber ones and celotex on youtube compared to a concrete pad. I tend to see concrete pads more with brick/block builds.
It's a balance. I preferred to do 30 holes rather than shift tonnes of land to get a level. It is no different than building a fence and the same tool kit essentially. Pads are a little bit out of favour because you lose a bit of height when you insulate them, or you dig down further. The costs add up vs. 400 quid of rods for my size build, a 65 quid ton of ballast and some cement.
How much gap did you leave from floor to the base timbers? I read that it should be 15cm to minimize splash back from rain?
I have an overhang of the roof of 15cm.left and right, 30cm front and back. So I'm out of splash zone. I hugged the floor as sensibly as I could so front left is probably 25mm from the ground -- I have a bit of work to sort out the adjacent land tho. I might add a stringer to the current beam and attach my decking directly to it though...
I understand how to do the risen timber floors and that air flow prevents damp with the PIR and tape creating a seal. But I don't really get the damp proof membrane vs damp proof course situation with using a concrete pad and just having the timber floor sat on top of it. Seems different methods can be used to prevent water wicking up the base.
For concrete you want a dpc in the middle of the pad. The dpc then folds up the walls to create a watertight structure. There are other methods but this is the one I've seen most recently... My workshop is concrete pads, 3 course of brick, dpc, then timber wall plate. It means I need a suspended wood floor or another concrete pour, or a PIR base and floating chipboard.
What have you decided on hot vs cold roof? I understand pros and cons of each but I think it will depend on my base choice first affecting height.
Hybrid. Basically smash the pir as tight to the roof OSB as possible. You can't do a proper roof under 2.5m.
Any ideas on predicted total cost and time? I gather EPDB roofing can't be applied with the glue when it gets uber cold come say October.
I'm probably 8k in at the moment but 3k of that was designer doors (3k). However that cost excludes cladding which'll be a fortune, internal insulation, internal plasterboard, electrics.... This is a large "do it once" type build tho, so I've maxed the plot vs. have a particular need for this size.
Why do you feel a steel lintel is necessary? (Not saying it isn't).
It's a 3m wide door sensitive to loads from above. I have doubled up 5x2 as roof joists so they weigh quite a bit.
Are places like Wickes pointless for decent timber at good prices? I find a lot of the CLS is heavily warped at my one.
No. Go to a merchant. Local family run ones can surprise you on how low they go.
You refer a lot to a "build pack" but I can't see where you state what this is, where from and how much it was. Is it some sort of kit from a supplier with a load of timber for this kind of project?
Oakwood garden rooms. They are 130 quid and include the bill of materials and some instructions that complement the yt videos.
How did you get a 70KG Rubber roof up a ladder by yourself?
As my neighbour put it "it was like watching an episode of worlds strongest man". It's heavy you just need to get it balanced on your shoulder.
Hope this helps - I know very little about concrete pads so I'm sure someone will correct what I've got wrong.
