Rebuilding a log cabin type summer house. Insulation advice

[adrspach]

Hi all. Before I get shot I did search for this type of advice but could not find anything specific to this style building. What I mean is T&G all around.

It is like this one.
https://www.waltons.co.uk/4m-x-3m-walto ... -log-cabin
The walls are 28mm T&G and floorboards are 12mm T&G.
The whole building is on 6"x2" rafters which I am planning to keep off the ground on pilots, on top of which there are 2"bearers. The ground I will cover with vegetation proof fabric membrane.
I just bought this second hand, took is apart and moved to our garden.
My plan is to insulate then floor before I built it up again as the rafters are crossed with bearers which could make it awkward to do once bearers are reinstalled.
At later stage I am planning to insulate the roof and walls depending how I can save money for materials.
Would I need different type of roofing cover rather than present felt?
My main worry is condensation as a lot of my tools in past suffered with rust and I would rather to make something that keep de-rusting my tools and equipment.
For the floor.
I was thinking about putting some battens inside of the rafters. Putting some sheet material on them to hold the insulation in place and put floorboards down.
If required where do I install the vapour membrane. How thick the insulation should be? Any cost effective options?
Thank you

 

[the_g_ster]

For the floor, be careful, don't create a bug and rodent nest by just hanging some lose insulation.

If you can, I would put some thin marine ply on the underside, well treated if vented under there and rainwater clears it should last well. Then some celotex inbetween, and then of course the flooring.

The walls are trickier....

If you think the walls will be clear of driving rain through the overhang of the roof, and sheltered from other buildings, then I would just line the inside with some battens and celotex and then some chipboard over the top.

If they are more exposed, then I would create an air gap between the outerface and an inner lining, vented at top and bottom, insect mesh on inside of vents. Then some battens to stop of the celotex touching the outer wall, then batten out and line. Dpm on the battens touching the outer wall will keep them dry too. You then have an air gap, stops moisture transfer and lets the outer face breathe.

Inside will be bone dry and warm, and cooler in the sun too.

If you wanted a few extra years you could treat the lower portion of the outer wall inside and out with preservative of some sort. May also be prudent to roller on an anti fire coating on the inside too, they are not expensive now.

Try not to break the insulation barrier too much with holes etc etc.

Get some work in progress pics up for us.

 

[jimmy_s]

Your vapour barrier should be installed on the warm side of any insulation.

 

[adrspach]

After 3 days of grafting I am a bit wasted.
The plan is the there will be the gap. Unfortunately after today's digging out of the platform next to a neighbours wall I have realised that the floor will be another foot higher that originally planed as the wall had steps in foundation built in therefore the brick lines are also stepped. Never mind.
I was planning on OSB boards 12mm underside. I will se if I can afford the Celotex or I need to look for options.
The rest will have to wait until I can save for it.

 

[adrspach]

Does the air gap have to be there on the floor too? Can the vapour barrier membrane touch the Cellotex or not?

 

[jimmy_s]

normally you have an air gap under the floor as well. Cellotex normally has a foil face which works as a vapour barrier - if but you can put one in touching the insulation.

The ventilation is to prevent interstitial condensation but this is more of an issue if the place is heated all the time.

If you have a construction in mind and if you want I can run Uvalue calcs and interstitial cond calcs if you want to be sure its ok.