Ideas for construction method on new summerhouse

[garyo]

I'm going to build a play-room summer house at the bottom of the garden this year. I'm putting it on the side of the garage so that I can have a link door. I want both to have a pitched roof which I'll cut over the top as a final step.

Other than that, I don't have much of a plan. I want the play room to be well insulated, so want at least 100mm to 1500mm of PIR foam in the floor, walls, and ceiling. The picture in my mind is traditional mass fill foundations with a concrete slab base, a dwarf wall three brick courses high, and then timber walls and cut timber roof.

On this basis, I'm lost on all the options for cladding, log lap, 50mm thick tongue and groove walls.

Connecting it to the garage means I don't want a pre-fab solution. Any recommendations on the most efficient sensible way of building this?

The room will be 5m x 4m. I'm aware of the regs and planning issues, but don't have experience of the various wall cross section, cladding, insulation details. What's your experience?

Thanks

Gary

 

[angelboy]

Someone of more experience might offer a better solution but I'd anchor the timber posts to the wall and continue the frame from there.

If you plan to use the room all year round and it's to be a habitable type space then unless your planning on an additional heating system then you won't have walls thick enough to meet the regs with timber cladding. If it's occasional use over the better months and is an incidental building then there's no requirement under the regs for any insulation at all so 100mm should be fine. You could always add an electic space heater at a later stage.

 

[garyo]

I'd anchor the timber posts to the wall and continue the frame from there.

That's my plan - but I'm not sure what to make the walls from. If I used traditional 100mm thick vertical studding then I could have 50mm of PIR between studs and 100mm of PIR over the top, then clad the exterior with something simple around 20mm thick.

Where I get unstuck is knowing whether, instead, I should build the walls from something more innovative, such as 80mm thick tongue and groove interlocking logs that you see. So the cladding becomes the structural wall, and then the PIR will be additional to that.

Gary

 

[angelboy]

Is that then partly a design consideration for it to be a log cabin? I don't know about those kits to be honest and I suppose the structural element depends on the roof covering as well.

Myself the plan is a single skin dwarf wall to 825mm, 1200mm of 100x50 C16 timber clad with 200mm feather edge or square edged pressure treated boards. I'm then considering battening out the internal timber by a further 50mm so that I can fit 150mm of insulation between the timbers and 50mm on the brickwork with 18mm ply lining.

I've not worked out any calcs and the building is primarily a shed which may be used for other things later in it's life. For this reason the floor doesn't have insulation but if it were to become an office or kids room then I'd add a 150mm floating floor later like you'd have on a garage conversion.

I think I'm trying to say that there are plenty of construction methods to achieve similar outcomes but it's dependent on what the building is to be used for, whether is under building regs and what the budget is.

 

[fmck]

This is a link to my on going (still!) summer garden room. It will be really only for the kids in summer so my insulation was pretty basic glass wool and concrete floor with no insulation. Its warm enough at the moment with a tiny oil radiator sitting at its lowest level. I am about to up date it and show the recent developments inside. Hopefully carpet tiles down this week and finish outside once the weather improves.


//www.diynot.com/forums/your-p...arage-with-garden-room-inc-store-room.361658/

There is also another summer room being built on the projects section you can probably find it easy enough.

 

[ban-all-sheds]

Where I get unstuck is knowing whether, instead, I should build the walls from something more innovative, such as 80mm thick tongue and groove interlocking logs that you see. So the cladding becomes the structural wall, and then the PIR will be additional to that.

You might want to look at some of the interlocking insulated wooden block systems - you might get some useful info from the Eden Center in Cornwall - I visited once and they had an exhibition of "green" building techniques, including 1 or 2 of those systems, so could be worth a phone call. Or try some of the eco/green building forums.

They are basically wood/insulation sandwiches, made to interlock - you just stack them up and you have a structural, insulated wooden wall. Quite popular in Germany.

 

[garyo]

Because it's going to share one of its four walls with an existing garage using a kit is out of the question. Also the pitched roof will integrate with the garage too.

It won't be subject to regs but I do want it to be well insulated and have future potential use as a home office perhaps, or a playroom/workshop for 9 months of the year. On that basis I want to be able to have a small electric fire to take the edge off the cold without it costing a fortune to heat, hence my intention to put 100mm of insulation under the floor and get it air tight as much as possible.

I think I'm trying to say that there are plenty of construction methods to achieve similar outcomes

I think you've hit the nail on the head there. I've built plenty of extensions to regs using traditional techniques... and in some ways that would be easier. Having a situation where I can do anything I want, and a market awash with pre-fab panels, cladding options, etc, isn't helpful!

I'll take a look at that link fmck, and at the interlocking blocks ban-all. Budget isn't too much of an issue.

Gary

 

[angelboy]

Personally, the design is the most important aspect for me followed by functionality which then allows me to think about the construction method which in turn can affect the budget. Sometimes I'll have the sacrifice one element for the other, such as my choice for the roof covering. I wanted to experiment with timber shingles but they were ridicimoney, something like £40/sqm (blooming slate prices) so I managed to source 4000 clay tiles for £6/sqm. Of course the roof timbers will have to be beefed up but once completed it should look like it's been there a while.

 

[joe-90]

Google 'sheds with beds'. That's what you are building.

 

[theoldun]

Gary,
See you are still trying to do your local builders out of earning a crust.
Will gladly give you some input if you answer couple of questions.
1. What W/m2K do you wish to achieve?
2. How many windows do you want?
3. Have you made up your mind on external finish?
4. Wall construction of existing garage? Am thinking of heat loss.
5. Has existing garage got a flat lid or duo pitched.?
Give us the answers and will give you a spec.
Regards oldun

 

[garyo]

Yep... still a fidget...

1. I'd like it to perform as well as, if not better than a well detailed cavity wall construction that uses lightweight blocks, so around 0.20 W/m2K.
2. I'd like a single pair of french doors on the south facing wall. Approx width 1600mm, but will depend on what eBay throws up I expect.
3. I'd not really made my mind up, but like the idea of some kind of stained wood - either horizontal or vertical orientation.
4. The existing garage wall will be one of the 4M walls and is made of a single skin of high density block with 15mm of render, so I'm expecting to need to clad this in PIR board of some kind.
5. Existing garage has leaky flat roof due to only dropping 40mm over 3M width, so my plan is to use the roofing skills you taught me to put a duo pitched roof over that (it already has beefy joists at 400 centres) , then have a valley and link it in to a duo pitch on the new summerhouse and have a hipped end. I like the idea of using something light like an EPDM roof covering over ply or OSB so that it's light enough that I can make the summerhouse with a vaulted ceiling on the inside and then leave a few feature joists exposed to stop and spread, but that's all a bit pie in the sky at the moment given that I've not even worked out the basics!

This is a rough sketch I did when I was considering making it out of blockwork with ~100mm of PIR cladding on the inside, and was considering a door through to the garage too so I can keep an eye on the nipper.

Untitled

• garyo
• 26 Mar 2014
• 1

The red lines are the roof outline. The extra overhang at the front is to cover an existing potting shed on the side of the garage and provide a bit of shelter over the front door.

Cheers

Gary

 

[theoldun]

Gary,
Very, very busy at moment so will do this in stages when ever have an hour to spare.
Slab.
Note in your first post that you mention traditional trench fill foundation.. You could do pads and ring beam but suggest you stick with traditional.
Trench 450 wide by 750mm deep and 600mm trench fill concrete, Go a bit deeper if ground conditions are not good.
Brickwork up to DPC level, two course above ground level, May leave you with step down into garage,
100mm MOT sand blinded,1000 gauge DPM over and turned up and over brickwork at DPC level, 100mm concrete. You will require a deadman each side when you concrete slab. If you not know what they are then say so.
That will then leave you with 100mm GA4000 Celotex and 65mm fibre screed.
Present L1B 2010 states U value of 0.22 W/m2K on ground bearing slab and with your P./L ratio of 0.90 LABC suggest that 75mm Celotex will comply, but for the extra few bob we go 100mm Celotex and will give U value of 0,20 W/m2K.
All we have time for to-day. Be back as soon as poss with super structure.
Regards oldun .

 

[garyo]

Thanks Oldun. I've not been on the forum for a while but I've been busy: Trenches are dug to your spec and I will mix/pour on Friday. It was hard work - it's very firm rocky clay.

I'm not sure what you mean by the deadman - presumably two bits of wood down either side to help get the slab level - something to rest the timber on due to the DPC level being 100mm higher than the top of the slab?

I agree I'll put 100mm of celotex on the slab too, on the basis that it will reduce wastage if the whole lot (floor, walls, ceilings) are done in the same 100mm.

Cheers

Gary

 

[theoldun]

Gary, Thought you had gone walk about.
Dead man. We use stiff concrete 450 wide and level from end to end down the edges, and possibly down the middle to split the bay and we screed of them. We use a 125x38mm aluminium rule laid flat and 900 bull float on 6m adjustable pole to finish..
As you will not have either of these. and working to concrete dead men is not at all easy, suggest you buy sufficient 47x125 timber to lay two number timber dead men against existing garage and mid span. Bed timbers to levels with hard packing every metre and throw couple barrows concrete down the edges to hold them in place.. When finished first bay, lift dead man against garage, remove packers, walk up channel with a dozen buckets concrete, fill channel and tamp and screed your way out. Use dead man for opposite side, then fill both channels as before. Clean up dead men as will use for stud work.
If you go this way, make sure top of slab finishes 175 below DPC and get rid of tamp marks.
Option 2. Leave your two course of splash brickwork of and screed concrete to top of brickwork. Run the two course of splash up to DPC when slab is complete Reduce celotex to 75mm (will still comply on your P/A) and 75 mm fibre screed
Will do your timber frame to-morrow.
Regards oldun

 

[garyo]

Thanks - I'm with you now.

I prefer the sound of Option 2.

Is it an option to lay chipboard flooring directly on to 100mm of PIR to minimise the amount of time the room would take to warm up? Or would that result in too much bounce in the floor (assuming I can get the levels to work out by using dead men)?