Summer house insulation

[JohnMo]

We just purchased a summer house, but will be insulating, and heating to make 365 day use. Will use single room MVHR or dMEV.

 

Floor insulation will be circa 150mm PIR with floating wooden floor. 

 

Roof will be warm roof, EPDM, OSB, PIR, breathable membrane(?), Tongue and groove 18mm timber. Does this sound about right?

 

Walls, are 70mm solid wood, wanting to add 50mm of insulation to inside and plasterboard.  Can I just add this inside the timber walls, or do I need a membrane or any air spaces?  Was wanting to screw through plasterboard and insulation into wall.

[Iceverge]

Do you have many electrics? Do you want them hidden or are you happy with conduits on the surface? 

 

Have you considered insulated roofing panels instead of a flat roof? It may be less labour? 

 

[JohnMo]

Good idea for the roof.

 

Not much electrics, just a light and a couple of sockets, and power for ventilation.  May run wires inside the wall blocks to hide it away

 

Heating likely to be UFH.

[Nickfromwales]

Noisy in the rain, that's the only downfall with those.

 

13 minutes ago, JohnMo said:

May run wires inside the wall blocks to hide it away

Best off with that, and have wall lights up lighting the ceiling instead of ceiling lights?

[Redbeard]

Walls are '70mm solid wood'. How can you run cables 'inside the wall blocks to hide it away'?

Or do you just mean stapled to the inside of the wooden wall and sandwiched between it and the insulation?

 

Is it too late to suggest you insulate externally? That way there's no interstitial condensation risk.

 

You said in your OP 'We just purchased a summer house'. Does that mean that any of us who are suggesting tweaks (roof sheets, for example, or EWI) are advising you to change something you can't change? (If you wanted EWI your roof would have to be bigger, and if your bought building already has a roof you won't want to be buying pre-insulated metal sheets.)

 

Can you give us more on what's possible to change and what's a no-go?

 

Thanks.

[JohnMo]

1 minute ago, Redbeard said:

Walls are '70mm solid wood'. How can you run cables

Drill holes in the blocks, as I build up the levels, so it makes a continuous long deep hole.

 

5 minutes ago, Redbeard said:

Can you give us more on what's possible to change and what's a no-go?

 

Roof build-up and how I insulate walls internally are are all open. Internal finish is going to be plasterboard, taped and painted.

 

I am ok loosing some floor space, but not too much height, hense external roof insulation.

 

External walls are staying as they are, so EWI isn't really an option. 

 

 

[Iceverge]

Ok I think I know where you're at.  You've bought something like the below off the shelf. It needs a base and a roof and you're planning on a thermal upgrade to boot?

 

[SteamyTea]

1 hour ago, JohnMo said:

Heating likely to be UFH.

Why not A2AHP.

Get some decent cooling then.

[Iceverge]

Ok how about something like this. 

 

For the walls from the outside in. 

 

70mm log construction. 

Chicken mesh stapled to the inner surface to prevent moisture being sandwiched between PIR and timber and to stop any water moving via capillary action. 

50mm pir screwed through to the logs. 

Vapour barrier taped to all edges or PIR boards diligently taped together. 

45x47mm battens with 50mm mineral wool 0.032W/mK infill.  Good as a service cavity also and no drilling of logs. 

Plasterboard. 

 

Total thickness about 180mm including logs. 

 

U value about 0.25W/mK

 

 

Roof construction sounds fine so long as you are diligent to ensure the vapour barrier is continuous from the walls to the roof.  

 

 

 

Assuming it is well orientated (south facing) it should need almost zero heating if it is small and you install MVHR. 

 

 

 

 

 

 

 

[JohnMo]

Thanks for the suggestions, never thought about chicken wire.

 

Fair bit of tree shading until mid afternoon, and about 5m by just under 4m footprint, double glazed windows.  The MVHR unit looks a good choice.

[JohnMo]

43 minutes ago, Iceverge said:

think I know where you're at

That's almost the same as ours.

 

31 minutes ago, SteamyTea said:

Why not A2AHP

That was the original plan, but managed to pick up a new ASHP that will do this and the house, for very little money.

[JohnMo]

So been reading up.

 

A log building like this can grow and shrink quite a bit.  Any battens directly screwed to the logs can place a restriction on this action and lead to splits and cracks. The normal way it seems to attach at batten is to use an angle bracket, this attached to the batten with two screws and to log with a single screw in a slot within the bracket, this allows the building to grow or shrink without effecting the internal wall.

 

The internal wall stops about 50mm short of full height and skirt is formed from the ceiling to cover the gap, as a sliding panel.

 

So my thoughts are a variation on @Iceverge suggestion.

 

Wrap the internal walls in a breather membrane. Then attach 100mm battens at 600mm centres via sliding brackets to the logs. Stop 50mm short of full height. Full fill with rockwool or similar up to roof.  VCL fully taped on walls and ceiling. Roof external 100mm PIR.

 

How does that sound?

 

[Iceverge]

On such a small building where you can personally control the quality would you consider with having the airtightness layer outboard of the insulation. 

 

How about. 

 

70mm logs, 

 

Taped breather membrane as airtight layer. 

37mm gap

63mm stand alone stud filled with 100mm batts "tucked around" the back of the timbers. 

 

plasterboard

 

It might work our as less in labour and materials?  

 

 

[JohnMo]

32 minutes ago, Iceverge said:

Taped breather membrane as airtight layer

Good idea

So just form standalone walls within walls, should be easy enough to do and zero strain on anything

[JohnMo]

Now started the build.

 

Base formed with 3x2 council slabs on concrete.  Asked for the bases to be flat and level, overall it not, there is 12mm run off over about 4m.  Compensated so far with shims.

 

So above the base to form a space for floor insulation, floor and an overhang for decking have built a frame using 2x 170mm X 45mm timber. This is under the floor framing that came with the kit.

 

Floor buildup will be as follows.

DPM, 100mm EPS100, 50mm EPS100, slip membrane, 2x layers of 9mm OSB, glued and screwed with staggered joints, 50mm battens at 400mm centers, infilled with 50mm UFH EPS mouldings, with UFH pipes at 115mm centres. This will be overlayed with tongue and groove flooring.

 

Overall there will be 200mm of EPS 100 insulation in the floor.

 

Walls next

 

 

[Iceverge]

47 minutes ago, JohnMo said:

DPM, 100mm EPS100, 50mm EPS100, slip membrane, 2x layers of 9mm OSB, glued and screwed with staggered joints, 50mm battens at 400mm centers, infilled with 50mm UFH EPS mouldings, with UFH pipes at 115mm centres. This will be overlayed with tongue and groove flooring.

 

Overall there will be 200mm of EPS 100 insulation in the floor.

 

 

Interesting. Please keep us updated with pics. 

 

Have you considered moving the DPM above one layer of EPS to prevent it getting punctured? 

 

How do you plan to run the UFH? 

[JohnMo]

1 hour ago, Iceverge said:

Have you considered moving the DPM above one layer of EPS to prevent it getting punctured? 

Good suggestion, just move the 50mm to the bottom, then dpm.

 

1 hour ago, Iceverge said:

How do you plan to run the UFH? 

Running pipes in this

https://www.thefloorheatingwarehouse.co.uk/product/thermrite-joisted-floor-insulation-panel-3-grooves-at-115mm-centres/

 

Simple 2 port manifold,  

https://underfloorheating1.co.uk/product/premium-2-port-underfloor-heating-manifold?/?utm_source=googleads&utm_medium=paid&utm_campaign=performance-max&gclid=CjwKCAjw5dqgBhBNEiwA7PryaEz_YJ3XV-YLCC8pyi_QoZP6WTWi1QF9p9tlzNyb1WMcRo0CyNccYRoCibkQAvD_BwE

 

Two loops of around 50m, driven by ASHP, giving heating and cooling.

 

[Iceverge]

I'm aware you want timber as a finished floor but I wonder if how it'd affect thermal performance of the UFH if one was to put the two layers of OSB on top of the profiled EPS. 

Something like:

 

50mm EPS

DPM

100mm EPS

50mm EPS with profiled boards with UFH

11mm OSB x 2 layers, glued and screwed.

Finished flooring. 

 

 

I'm just wondering could it be an alternative to a concrete floor for those who want UFH and are limited in the space build-up or those who like me are not a fan of the hardness of concrete floors. 

 

 

 

 

[JohnMo]

Some progress today before the rain.

 

[PeterW]

3 hours ago, JohnMo said:

Some progress today before the rain.

 

Is that from Tuin..?

[JohnMo]

No, your the second to ask that today.  It's from gardenhouse24.

[joe90]

3 hours ago, PeterW said:

Is that from Tuin..?

Interesting as I am looking at a log type garage from “quick garden” and thought I would look at the Tuin site mentioned by @PeterW above. The Tuin site gives a guide on planning etc but I am not sure they are correct, quote…..If you’re within 2m, measure from the boundary to the 2m point, if you’re below 2.5m it’s officially a ‘permitted development’, even if your ridge height extends above 2.5m. 

I am not sure that’s correct, from the planning portal sectionE (garden buildings/garages etc) states…” If any part of the building, container or enclosure is within 2 metres of the boundary of the curtilage of the house, then the height limit for the total development is restricted to 2.5 metres if it is to be permitted development.”

 

note particularly the “if within 2 meters of the boundary (which mine will be, but more than 1m ) then the 2.5m height limit is for the whole development”. 
 

anyone?

Edited March 20, 2023 by joe90

[Iceverge]

Seems a shame to cover up all that lovely wood with insulation now!

 

I assume the boards at the base will disappear once the concrete has cured further?

[JohnMo]

7 hours ago, Iceverge said:

 

I assume the boards at the base will disappear once the concrete has cured further

The boards at the base are there for ever.  That is the base frame the cabin sits on and will be filled with insulation inside and form the floor.  The bits at the front will never be seen as there will be a cantilevered small deck with a step hiding it.

[JohnMo]

Day 2 progress.

 

Stripped walls down to board level 3 (removing about 7 layers) as one of the logs was twisted and caused a big run off at one corner.

 

Built the walls back up and now at roof level.  Used the twisted logs at the higher levels, bit of a faff but all good.