Ask The Trades - Few decking/log cabin questions

arin

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Few decking/log cabin questions
Feb 4^th, 2014, 10:28am

We have had a log cabin build for some time now. Came as a kit but was never insulated.

it is build on a concrete embedded post system raised rafters - cabin built on raised rafters, so does not touch the floor.

There is an open crawl space under the floor which is installed.

this open crawl space is shingled.

What are my options to insulate the floor and roof?

I would like to do as less work as possible - i.e. not remove roofing etc

For the roof can I Batton to create air gap of 40mm install celotex on top inbetween rafters on the inside?

or do i need to install a moisture barrier?

the roof currently is t &g boards on top of the rafters with rubber type tiles? - not too sure if there is a lining under the tiles though?

flooring - whats my best option? can i just install celotex right on top of the existing floor and then install more floor (boarding) over the celotex.

or should i lift up the flooring - batton across rafters and lay celotex underneath the existing flooring and then re lay the flooring down?

do i need a damp proof membrane here?

finally i'd like to build a side shed out of timber. I would be laying on existing decking which surrounds the 'log cabin'.
can I build my floor frame directly on to the decking as it is? or not?
what are my issues with that?

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woodsmith

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Re: Few decking/log cabin questions
Reply #1 - Feb 4^th, 2014, 10:48pm

It's very difficult to give any sort of definitive reply without seeing the cabin, but basically moisture barriers are needed if warm moist air can reach a cold surface. As for the flooring if you have enough headroom you could put Kingspan type insulation on the floor and fit sheet flooring on top rather than try to floorboard over it.

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arin

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Re: Few decking/log cabin questions
Reply #2 - Feb 4^th, 2014, 11:09pm

Hi, thanks

ill get some photos tomorrow.

I do have the space to put kingspan directly on the floor and then perhaps laminate over it - except its used as a gym currently so heavy items are placed on the floor.

is this still ok?

As for the roof i intend to batton inside along inbetween rafters to leave an air gap of 1"-1.5". put sheets of kingspan on the battons and panel over the rafters to hide the ugly insulation.

I will install small air vents to vent air between both ends of the rafter lengthways so that air can flow between the air gap and outside easier.

is this ok for a cold roof?

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arin

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Re: Few decking/log cabin questions
Reply #3 - Feb 5^th, 2014, 12:15am

woodsmith wrote on Feb 4^th, 2014, 10:48pm:

It's very difficult to give any sort of definitive reply without seeing the cabin, but basically moisture barriers are needed if warm moist air can reach a cold surface. As for the flooring if you have enough headroom you could put Kingspan type insulation on the floor and fit sheet flooring on top rather than try to floorboard over it.

can i not then place insulation directly on to the internal roofing then moisture barrier the entire roof (over rafters and insulation) before its finished in plasterboard or panelling?

or would this mean the insulation would rot?

is a moisture barrier an AIR BARRIER? or VAPOUR BARRIER?

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scotspark Trade Member Offline mmmmm it's gonna cost you!! Posts: 3074 Total Thanks: 10 For This Post: 0 scotland Scotland Gender: Trade: Electrician	Re: Few decking/log cabin questions Reply #4 - Feb 5^th, 2014, 12:16am yes that would be the method or use foil backed plasterboard
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arin GDPR opt-out Total Thanks: 10 For This Post: 0	Re: Few decking/log cabin questions Reply #5 - Feb 5^th, 2014, 12:20am am i not then locking the moisture into the insulation and rafters and roof causing problems?
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arin

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Re: Few decking/log cabin questions
Reply #6 - Feb 5^th, 2014, 12:32am

Quote:

Hi, thanks

ill get some photos tomorrow.

I do have the space to put kingspan directly on the floor and then perhaps laminate over it - except its used as a gym currently so heavy items are placed on the floor.

is this still ok?

As for the roof i intend to batton inside along inbetween rafters to leave an air gap of 1"-1.5". put sheets of kingspan on the battons and panel over the rafters to hide the ugly insulation.

I will install small air vents to vent air between both ends of the rafter lengthways so that air can flow between the air gap and outside easier.

is this ok for a cold roof?

this is cheaper and easier though? i.e. no expensive vapour barrier or foil plasterboard - will this not work?

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woodsmith

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Re: Few decking/log cabin questions
Reply #7 - Feb 5^th, 2014, 11:13pm

A vapour barrier is needed to stop moisture in the air (which is inside the building) travelling through or past the insulation and condensing on a cold surface within the wall/roof.

You can't fit laminate on top of insulation, you would need to fit a boarded floor over the insulation and then lay laminate over that.

If you plan to put heavy equipment or have a lot of people/weight on the floor you would need to fit battens the same thickness as the insulation within the insulation.

If you fit Kingspan as you suggest in the roof, leaving an air gap above which is well ventilated, then the roof should be OK as long as the covering material is perfect and has no leaks. This sort of arrangement could potentially allow a leaking roof to go unnoticed until it has caused a major problem.

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arin

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Re: Few decking/log cabin questions
Reply #8 - Feb 6^th, 2014, 2:08am

woodsmith wrote on Feb 5^th, 2014, 11:13pm:

A vapour barrier is needed to stop moisture in the air (which is inside the building) travelling through or past the insulation and condensing on a cold surface within the wall/roof.

You can't fit laminate on top of insulation, you would need to fit a boarded floor over the insulation and then lay laminate over that.

Then am I better off (cost wise) to lift up the floor chicken wire the underside of the rafters fill with rockwool insulation and re lay the floor

the underside of the chicken wire being free flowing air - moisture would get there but water itself wouldnt - thus the insulation would never get soaked/wet.

Also, in roof do i vent airgap and vent upper roof space (underside of ceiling) to avoid moisture build up on my plasterboard facing in?

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woodsmith Global Moderator Trade Member Author Offline Posts: 4395 Total Thanks: 135 For This Post: 0 Gender: Trade: Joiner	Re: Few decking/log cabin questions Reply #9 - Feb 6^th, 2014, 7:04am For the floor, it all depends how easy the existing floor will come up. For the roof, if you mean, do you ventilate between the insulation and plasterboard, then no, that would defeat the object of the exercise.
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arin

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Re: Few decking/log cabin questions
Reply #10 - Feb 14^th, 2014, 6:37pm

if the existing floor doesnt come up easy - laying kingspan - battoning between for support of above floor and then relaying over the top is the option?

do i need to leave airgap here like i would for the roof?

or is it simply - crawl space(open) - t & g external floor - kingspan/support battons - t&g flooring?

thanks

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woodsmith

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Re: Few decking/log cabin questions
Reply #11 - Feb 15^th, 2014, 8:02pm

No you don't need an air gap but it may be worth putting a vapour barrier over the insulation, you may not need it with a well ventilated space under the floor but is only cheap and will stop condensation forming on the existing floor. For t&g you would be better off with t&g chipboard, 18mm if it is lightly loaded or22mm if more heavily loaded.

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