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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Carpentry Questions >> Log Cabin Insulation https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1248189173 Message started by joBie on Jul 21^st, 2009, 4:12pm

Title: Log Cabin Insulation
Post by joBie on Jul 21^st, 2009, 4:12pm

Hi I’ve bought a summer house (outdoor room), could some one suggest the best way to insulate it ...Firstly the ground ?
Many thanks in advance!! JoBie.

Title: Re: Log Cabin Insulation
Post by woodsmith on Jul 22^nd, 2009, 7:49am

Kingspan, (foil backed thermal board) is probably going to be the way to go. If you can fit it tightly between existing battens then clad over the top that would be the easiest and most effective option. You will need to fit a vapour barrier between the insulated wall and the INSIDE cladding.

As for the floor if you can insulate under the floor in the same way as the wall then that is the quickest option. If the floor is already down then you could lay a floating floor (loose lay 25mm Kingspan and cover with flooring grade t&g with the edges thoroughly glued) but you would lose 50mm o0f headroom this way. Again you would need a vapour barrier and if you plan to have heavy items in the room lay 25mm battens round the edge of the insulation under the chipboard.

Title: Re: Log Cabin Insulation
Post by CWatters on Jul 22^nd, 2009, 10:36am

How big is it? If it's bigger than 15 sqm it needs to be located >1 meter from the boundary of your garden or Building Control need to be involved. Presumably it's not bigger than 30sqm?

What make is it? Sometimes the manufacture has optional insulation and might be cheaper to buy that?.

What's the wall construction? Ideally you should have a 25-50mm ventilated cavity between the insulation and external cladding to help prevent condensation but that would probably stop you fitting as much insulation in. If you are happy to loose a bit of space perhaps put 50mm between the studs and another 25-50mm on the inside - but possible issues with door and window openings? Perhaps worth taking a risk and just filling the wall.

The vapour barrier on the inside is typically a plastic sheet from screwfix stapled up.

Plan the electrics before you insulate. It's nice to have lights and a socket for the hifi, possibly also a network point for your laptop out there. As a minimium you might consider installing a short length of water pipe and or conduit in the ground/wall before insulating and boarding the inside. That way you can push wires through later. Otherwise get an Part P electrician to comment on what prep to do when he comes round to quote.

Title: Re: Log Cabin Insulation
Post by joBie on Jul 23^rd, 2009, 10:35am

Hello again ;D
Woodsmith yep Kingspan will be the way forward for the walls but
my problem is the floor bearers sit directly on the concrete flags with 19mm tongue and groove floor boards on top , I’m thinking to put something on the concrete in between the bearers so I don’t lose any height in the cabin. Plus I don’t want the wild to be warm an comfy.

B+Q are selling off a concrete floor sealant £19.99 a tub would this help in any way?

CWatters Its a dunster house 4.5m x 2.5m 14ft 9”X 8ft” I should be alright with planning perdition so they say :-/ it arrives on the 30th perhaps I will ask them regarding the insulation I now more clued up on the price. Good idea I will put the conduit in while insulating.

http://dhlogcabins.co.uk/uk/product/247/1883/45m-x-35m-lantera-a-45mm-walls-double-glazed
Seems to be the best price on the market for a Diyer.

THanks again fella's for the good advice !!!

Title: Re: Log Cabin Insulation
Post by woodsmith on Jul 23^rd, 2009, 7:15pm

I don't think the sealant would help but;

You could lay battens (I've done something similar and used decking boards) under the bearers, at 90 degrees, and that would allow you to fit Kingspan between the bearers with the battens keeping it off the floor and allowing air to circulate underneath. That way you don't lose any headroom. If you do this it a vapour barrier over the bearers before you lay the t&g floorboards.

Title: Re: Log Cabin Insulation
Post by CWatters on Jul 23^rd, 2009, 7:19pm

Quote:

This cabin is under 2.5m tall to comply with new planning rules.

Humm that's not the whole story. You can have a taller outbuilding if you follow the rules here..
http://www.planningportal.gov.uk/england/genpub/en/1115315233153.html

These sorts of buildings aren't really designed to be insulated. If you just slap in some insulation there is a small risk that condensation might form between the insulation and the log walls. The vapour barrier on the inside should stop warm humid air from the room getting to this place but some damp air can still get in from the outside. Most people get away with it, but a few have a problem.

If you wanted to be 100% sure this couldn't happen you would need to space the insulation off the walls as I mentioned above and ventilate that cavity to the outside. Likewise when you line the roof. Perhaps you prefer to take the risk though.

Either way if you are sealing up the building with insulation and vapour barriers you should also ventilate the room itself to the outside if there aren't trickle vents in the windows.

Title: Re: Log Cabin Insulation
Post by CWatters on Jul 23^rd, 2009, 7:26pm

It might be possible to build the floor then get a mate to help stand it on edge. Fix the insulation to the underside lay it back down.

I'd be tempted to put the bearers on bricks or blocks rather than slabs to raise it up a bit more (or perhaps just two layers of slabs?). Putting some DPC between the blocks and floor bearers would also help

Title: Re: Log Cabin Insulation
Post by joBie on Jul 25^th, 2009, 11:17am

Hi again :) having some spare paving bricks 2 and a half inch already in the garden I’m now thinking of jacking it up one course consequently I can put pea gravel on the concrete flags around the structure apparently this will help with the runoff plus the rain splash back.

What is Dpc ?

I suppose I can tackle the wall insulation from inside at a later date, although when buying the Kingspan for the floor do I buy/ use it for the roof also ? under the roofing shingles?

Thanks XXXJoBiEXXX

Title: Re: Log Cabin Insulation
Post by sparky415 on Jul 26^th, 2009, 10:02am

DPC is damp proof course

http://www.screwfix.com/prods/83999/Building/Damp-Proof/Damp-Proof-Course-225mm">http://www.screwfix.com/prods/83999/Building/Damp-Proof/Damp-Proof-Course-225mm

I have looked at the link for the cabin (looks great) did you spot
that they do their own insulation kit?

As CW said earlier now is the time to think and plan the electrics
What are you going to use the room for?
How will you heat it so you can use it all year round?(the size of feed cable will depend on this)
Future office?
Phone line?
Fuse board?
Sockets?
lights?
Outside light with sensor?

I would draw a little plan :)

Title: Re: Log Cabin Insulation
Post by joBie on Jul 29^th, 2009, 2:34pm

Hi folk's, with the structure only having a single skinned wall does anyone think I could put wooden battens up then spray the walls with expanding foam for better insulation ?

Hi Sparky yes I did spot that they do their own insulation its seems it with all their extras!!

The room is going to be my art room with electrics internet and a rowing machine.
Two plug sockets either side and central light.
Heating don’t know yet perhaps oil radiator,
so far two low wattage lights on the outside that go off at dawn but I would like to switch them on and off when I want, un like that bloody 500 what security censer light that keep coming on and stays on all night :( think it’s the weather.

Would silver armored cable be Ok up to the cabin and around the garden ?

[size=14][/size]

Title: Re: Log Cabin Insulation
Post by CWatters on Jul 29^th, 2009, 3:39pm

I'd steer well clear of spray on foam. Makes a right mess and the density isn't as well controlled as factory produced insulation like Celotex or Kingspan. Although expensive those are the best insulators available for a given thickness. The only thing better is Aerogel and that's v.expensive.

The regulations give two options for the electrics, either:

a) Use a Part P electrician to do it all.
b) DIY and make a Building Control Application

You might find a) is cheaper if you offer to dig the trench from the house to the cabin. Ask the electrician when he comes to quote.

Title: Re: Log Cabin Insulation
Post by CWatters on Jul 29^th, 2009, 4:39pm

Lets do some numbers to work out how thick the insulation needs to be to give roughly the same level of insulation as the wall of a new house...

The web site for the cabin says the walls have a U-Value of 1.9 W/m^2K.
I believe a new house typically has walls with a U-Value of around 0.27 to 0.3 W/m^2K. Lets call it 0.27.

First convert both of the above to Thermal Resistance = 1/U-Value...

Cabin walls have a thermal resistance of 1/1.9 = 0.53
New house wall thermal resistance is 1/0.27 = 3.7

That means the insulation and plasterboard must add 3.7 - 0.53 = 3.17

I think plasterboard has a thermal resistance of about 0.06 meaning the insulation must provide 3.17 - 0.06 = 3.11

Celotex/Kingspan type foams have a thermal resistance per meter thickness of about 43 so you need around..

3.11/43 x 1000 = 72mm

So something like 70mm Celotex GA3000 or Kingspan K8 would seem to be ideal. You could fit less and the results would be roughly in proportion to thickness. (eg half as thick would be roughly half as good). Upto you really.

If that's too expensive I would look at http://www.secondsandco.co.uk/ to see if they have anything close.

Title: Re: Log Cabin Insulation
Post by sparky415 on Jul 29^th, 2009, 6:40pm

Quote:

Hi Sparky yes I did spot that they do their own insulation its seems it with all their extras!!

Sorry I don't understand this :-?

The silver cable you mention, the only silver one I have seen is armoured flex
I was thinking of 'SWA' steel wire armour

Title: Re: Log Cabin Insulation
Post by sparky415 on Jul 29^th, 2009, 6:50pm

CW,

I had to look up 'Aerogel' on tinternet
clever stuff bet it would cost an arm an leg to wrap my house in it :(

http://www.aerogel.com/

Title: Re: Log Cabin Insulation
Post by joBie on Aug 3^rd, 2009, 10:14am

Yes sparky it is the 'SY/NR 3 core steel wire armored.

I’m going to go for the Kingspan its clean and lightweight to maneuver.

We meet again :) CWatters I’ve had a look at seconds and co they would charge for delivery it so it evens its self out, a friend dropped 4 sheets off in his van I paid top wack  your calculation are impressive thanks I’ll tackle the insulation when I can it at a better price !!

It arrived on Thursday in the bloody pouring rain, had to put it in next doors garage while I got it sorted and toweled dried now in bits all over the house.

Just a thought while I’m waiting for a break in the weather like next week should I paint the clear preservative in between the tongues and groves would this cause it to warp ?

Being a cheap skate Aeroge is cool but I’m running out of budget :([size=14][/size]

Title: Re: Log Cabin Insulation
Post by sparky415 on Aug 3^rd, 2009, 12:22pm

I got a feeling that you are referring to armoured flex not 'SWA'
I also think it will be a lot more expensive than SWA

.....probably

Title: Re: Log Cabin Insulation
Post by joBie on Aug 12^th, 2009, 9:41am

HI Sparyk, I got it fee from a neighbour :)