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Old 21st Oct 2018, 10:01 am   #61
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Default Re: Thermal insulation for a wooden shed: advice, please.

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Originally Posted by mark2collection View Post
A dehumidifier is a good idea, go for a desiccant type, not a compressor type.

The desiccant type will happily work below 10 degrees C with the added bonus of generating heat, the compressor type will just ice up & eventually wreck itself.

The one I use is an Ecoair, plus a wall mounted oil radiator from Screwfix, the room stays a comfortable 19 degrees at 60-odd % relative humidity.

My old compressor dehumidifier was useless in the winter, the radiator would pump out heat, the dehumidifier would chuck out cold air and in the end, ice up. The new desiccant one is brilliant, the radiator isn't working nearly so hard either.

Mark
Surely a compressor type dehumidifier also generates heat? Heat is removed from the condensing coils and given out to the atmosphere, just as with a domestic fridge. The compressor motor will also give out heat.

If the condensate pipe is properly lagged, there's no reason why icing up should occur.

I too am an Ebac fan. No pun intended.
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Old 21st Oct 2018, 10:50 am   #62
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Default Re: Thermal insulation for a wooden shed: advice, please.

Tools always rust in the garden shed was the basis for me researching into condensation about 15 years ago when I built my Observatory here in the West of Scotland. In the UK condensation is a real problem for Observatories as they must be kept as close to the outside ambient air temperature but without condensation forming on the very expensive computers, cameras and Telescope Mounts therein. The solutions to control this are exactly the same for workshops, but first a word on condensation but without going into too much detail on the dew point. Basically the air around us is like a sponge and the warmer it is the more moisture it can hold, however as nighttime approaches and the air cools the sponge get wrung out and water starts appearing on cars etc etc. An even worse weather scenario is when a warm front arrives after a cold one and objects that have mass drip with condensation. This of course applies to the whole country though it can often be missed as many of us go to work and don't see this first thing in the morning but it does explain why tools eventually rust in the garden shed. To avoid this any shed that is hermetically sealed as best possible with a desiccant type dehumidifier running in the background is unlikely to suffer rust issues. I use a Ruby Dry myself but there are plenty to choose from.
For information I don't heat my Observatory, it's un-insulated plywood covered in butyl rubber and I'd suggest if it works here in the damp West of Scotland the solution will work anywhere but the key is keeping the outside air out and the inside air.
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Old 21st Oct 2018, 12:38 pm   #63
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Thumbs up Re: Thermal insulation for a wooden shed: advice, please.

Suggestions for a de-humidifier: all read. Thank you.

Al.
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Old 23rd Oct 2018, 8:14 am   #64
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Default Re: Thermal insulation for a wooden shed: advice, please.

Al,
You asked what type I have. Is an Ecoair, with both tray and external pipe outlet. Cost about £100 if I remember correctly. Has run without problem for three years now.
Regards,
Richard
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Old 23rd Oct 2018, 8:50 am   #65
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Default Re: Thermal insulation for a wooden shed: advice, please.

Just to let you know, the B&Q one is currently reduced to £89, found out yesterday as it looks like we are going to need more than one in our house!

Regards
Lloyd
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Old 24th Oct 2018, 5:08 pm   #66
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Question Re: Thermal insulation for a wooden shed: advice, please.

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I always recommend a unit that displays temperature, humidity and dew point: http://www.extech.com/display/?id=14270
ExTech Humidity Alert II; 445815.
Yesterday, I had mine delivered. I could with a bit of guidance on using this item, please.
You're aware of the environment this item will be used in. (Currently without thermal insulation: due to arrive soon!).
With this item, you can set %RH alarm limits.
What would be sensible limits to set?
Why is there a MAX. and a MIN. limit?

I'm a bit of a novice at this 'environmental control' business, (but I do understand 'dew point'), so any advice will be welcome.
Thank you.

Al.
Oct. 23rd.
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Old 24th Oct 2018, 5:11 pm   #67
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Arrow Re: Thermal insulation for a wooden shed: advice, please.

Re: post #64. Thank you, YoungManGW / Richard.

Al.
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Old 24th Oct 2018, 5:42 pm   #68
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Default Re: Thermal insulation for a wooden shed: advice, please.

Re. post #66: I've got an Ebac "PowerDri Professional" in the house here - and various humidity-indicating devices. During the summer it stays off (doors and windows are open - why try to dehumidify the planet?) but since the beginning of the month it's come out of its summer-rest because the RH in the house was around 75%.

Running it on 'max' it's been dragging at least five litres of water per day out of the air for the first couple of weeks; now it's down to 3 litres a day and overall RH is down to around 60%. I'll be leaving it doing its thing until I get the RH down to around 45%, which I always feel happiest in in winter.

50% RH is a good target to aim for: it 'feels' dry but you won't suffer any problens with static or wooden cabinets shrinking/warping.

Remember that when you condense atmospheric damp to water, you recover the 'latent heat of vapourisation' in the process - so a dehumidifier is actually gaining you heat over and above the number of Watt-Hours of electricity it consumes.
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Old 24th Oct 2018, 7:06 pm   #69
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Default Re: Thermal insulation for a wooden shed: advice, please.

Quote:
Originally Posted by Skywave View Post
Quote:
Originally Posted by mhennessy View Post
I always recommend a unit that displays temperature, humidity and dew point: http://www.extech.com/display/?id=14270
ExTech Humidity Alert II; 445815.
Yesterday, I had mine delivered. I could with a bit of guidance on using this item, please.
You're aware of the environment this item will be used in. (Currently without thermal insulation: due to arrive soon!).
With this item, you can set %RH alarm limits.
What would be sensible limits to set?
Why is there a MAX. and a MIN. limit?

I'm a bit of a novice at this 'environmental control' business, (but I do understand 'dew point'), so any advice will be welcome.
Thank you.
I haven't made use of the alarm facility.

If the RH becomes too low you might get problems with static or dry eyes. Unlikely in this context, of course.
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Old 27th Oct 2018, 9:42 am   #70
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Default Re: Thermal insulation for a wooden shed: advice, please.

As has been said above, 50% RH is a good target to aim for. Computer Halls are set to 50% to obviate static problems and makes for comfortable for working in.
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Old 29th Oct 2018, 12:33 am   #71
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Default Re: Thermal insulation for a wooden shed: advice, please.

Just done a crude thermal test on my new shed- trapezoidal plan 12' wide at front, 8' wide at back and 8' deep, roof and walls insulated with 55mm foil faced Kingspan. Standard sized solid wood door and about half a square metre of single glazed window. Floor just 19mm ply on treated wooden supports above concrete base.

750W from small convector heater was enough to get the inside temp at waist height up by at least 20C above outside ambient.

Good enough for its intended use as occasional guest bedroom!

Sounds like an 800W or so dehumidifier would also provide adequate heating on its own if condensation turns out to be a problem.
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Old 2nd Nov 2018, 11:40 pm   #72
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Default Re: Thermal insulation for a wooden shed: advice, please.

Hi

I have now completely dismantled my old workshop which was attached to the garage wall and had problems with the roof and mould etc. I am planning the layout for a new workshop and would like to ask a few questions.

It will be a fairly small workshop about 9' x 5' (2.7 x 1.5m) and I'll be utilising the old floor structure which is in excellent condition. I do intend to insulate this though with Celotex 25mm thick foil backed insulation board fitted between the joists and flush with the underside of the OSB.

As for the walls, I'll be using 50mm square section treated sawn timber. On the outside of the frame will be a breathable membrane. Either shiplap or feather edge timber cladding will be used over the membrane. The inside will again have 25mm thick Celotex insulation. The walls will be lined with 6mm or 10mm plywood. Does this seem a reasonable way to build the walls?
My main concern is the type of breathable membrane to use. Most products appear to be specified for roofs some seem to be suitable for both walls and roofs. Would this product https://www.screwfix.com/p/cromar-ve...1m-x-25m/1349p be suitable to use for the walls?

I'll be installing opening timber windows on three sides of the workshop. These will be obtained from here https://www.windows4sheds.co.uk/prod.../details/#WFL2. These look to be good value for money.

As for the roof, 18mm OSB will be covering the roof framework, again, with a breathable membrane over the board. On the inside of the roof Celotex will be used and lined over with plywood. On the outside, Onduline corrugated bitumen sheets will be applied over the membrane. Does this seem OK?

I'll be using small supporting battens to set the insulation board in the correct position maintaining a reasonable gap between it and the membrane. In effect, the insulation boards will come flush with the inside of the timber frames.

Re. the breathable membrane, DuPont's Tyvek Housewrap is a good product but is a little pricey, and supplied in a rather large quantity so I wondered if the Cromar product in the above link would do for the walls and the roof of my new workshop?

One other question, I intend to make a new base for the workshop as well. This will be a 2" thick sub base of aggregate whacked flat with paving slabs cemented on top. Regards the sub base, 40mm to dust is often quoted as the recommended grade to use. I wondered if 3/4" or 19mm to dust would be suitable for my requirements?

Adding up the costs of the materials soon mounts up and nothing is cheap these days. The shiplap cladding is quite expensive so may go for feather edge instead. All told, I don't expect to have much change out of £1000 time its all built. Hopefully it will all be worthwhile though and give many years of service.

Regards,
Symon

Last edited by Philips210; 2nd Nov 2018 at 11:49 pm.
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Old 3rd Nov 2018, 12:27 am   #73
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Default Re: Thermal insulation for a wooden shed: advice, please.

The first thing that leaps out to me is the 50mm sawn timbers. Of course, it depends where you buy them from, but certainly the sort usually found in the DIY "sheds" is usually pretty horrible. OK, they will be hidden, but they are rarely straight and give out splinters for fun.

Personally, I'd recommend "CLS" timber - for example: https://www.wickes.co.uk/Products/Bu...mber/c/1000201 - it's not terribly expensive compared to the sawn stuff when you consider how much better it is. I usually buy mine from a builders merchant, but when I've got odd bits from B&Q, it's been OK. The stuff from the former is usually treated. You should be able to find it in 50mm square (47mm IIRC) with no problem, but going for "2 by 3" allows more space for insulation and results in stronger walls (it's the minimum I'd use).

Don't forget the plastic vapour barrier on the warm side of the insulation - that's more important than the breathable building paper on the outside IMHO. Given good quality cladding with a decent overlap, I'm not completely sure you need the paper, but I guess it's a useful "second line" defence, especially if you live in an exposed area.

The foil backing on insulation sheets is only good as a vapour barrier if you seal all of it together using aluminium tape where it crosses the timbers, etc. Given that plastic vapour barriers are really cheap, it might be more economical to use that instead of buying several rolls of aluminium tape (although places like Lidl/Aldi often have it cheap).

I'd be tempted to use plasterboard rather than ply for the walls, mostly because it's easier to finish. It's much cheaper than ply, and at the suggested thicknesses, it's probably not much weaker either. Of course, you'll be screwing through into the studs, so as to maintain the vapour barrier as best as you can, so the thickness of the material is probably not important. Plasterboard adds some insulation value, but most importantly it helps to slow the spread of fire. Doubling it up helps with that (along with noise and thermally too).

Most cheap sheds use 12mm OSB for roofs. The thickness required really depends on how spaced out the support joists are - something the cheap sheds really skimp on IME. Using more CLS timbers might bring other benefits besides allowing for thinner sheeting, such as making it easy to store things in the roof space, perhaps...

You might be able to get the cladding at a better price from a fencing supplier - at least, that's what I've found around here for feather edge. For getting the best prices, I've found that it's best to approach the local builders merchants and play them off against each over. Mid-morning is often a good time, after the morning rush. It's not something I enjoy doing, but asking for discounts usually works if you're nice about it and buying a reasonable quantity. It's frustrating to know that most builders are paying considerably less than the likes of us, and no-doubt not doing as nice a job with the materials as we will Sometimes, the "sheds" can be cheaper and just as good for certain items, so it pays to shop around if you aren't in a rush.
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Old 3rd Nov 2018, 12:50 am   #74
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Default Re: Thermal insulation for a wooden shed: advice, please.

That's good advice Mark.

I had considered using CLS which I've used successfully in the past but I'm limited for space. The 5' or 1.5m side is located between the garage end wall and the boundary wall and will probably need to be built about 4" less as I need to maintain about 19" access on both main sides. Using CLS will effectively reduce the internal space further. I agree CLS is decent timber to use and mostly straight and well finished. If I had more space to accomodate a larger workshop then I'd use CLS.

That is also a good point about a vapour barrier. Yes, aluminium tape over the joints is a good way to go.

I think the membrane over the outside of the studs will be needed as the weather can be quite grotty and I don't trust the cladding to be 100% effective in keeping out the rain.

My original workshop used a sand coated roof felt over the outside of the studs which did a good job keeping out the rain but wasn't breathable so didn't allow water vapour to escape. I just wondered if the Cromar made membrane would be suitable.

Regards
Symon.
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Old 3rd Nov 2018, 10:36 am   #75
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Default Re: Thermal insulation for a wooden shed: advice, please.

Hi.

With regard to the CLS timber, I was basing my assumptions on the 38 x 89mm size but didn't realise there's a 38 x 63mm section available. This would be preferable to the 50 x 50mm (actually 45 x 45mm) sawn treated timber. The only down side is where sheets have to join on the studs, there's only a 19mm overlap each side of the joint. I guess extra noggins could be used in some circumstances. I'll be looking at using this smaller CLS section for the studwork as it has a consistent section, is straight, and quite reasonably priced. Scant timber is another option but will have to look into the available sections.

Regards
Symon.
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Old 3rd Nov 2018, 11:45 am   #76
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Default Re: Thermal insulation for a wooden shed: advice, please.

Which firm are you getting your timber from?

Lawrence.
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Old 3rd Nov 2018, 12:30 pm   #77
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Default Re: Thermal insulation for a wooden shed: advice, please.

Tyvek's good stuff but is expensive, a lesser known brand can be used, as an example about 5 years ago I started to build a small pent roof shed at home to store some gardening stuff in, concrete base, single course of blocks, stud walls on top of that then roofing sheets, fitted a breather membrane on the outside ready for cladding and filled the shed up with "stuff"....5 years on, still not clad The original membrane is still on the outside, survived some horrendous weather and amazingly hasn't ripped nor leaked, that was UV15 (TLX) the black stuff.

Lawrence.
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Old 3rd Nov 2018, 1:08 pm   #78
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Default Re: Thermal insulation for a wooden shed: advice, please.

I've got some scraps of left over 45mm x 45mm CLS in front of me. 45mm is the actual measurement that I've just done - I think it's sold as 47mm x 47mm IIRC. Easy to find in the local builders merchants, and not at all expensive

I'd still recommend "2-by-3" (my samples measure 45mm by 68mm) if you can accommodate it. Even in a small space, an inch is not much to loose.

Sorry - I have no experience of the Cromar membrane. My concern about any sort of membrane on the outside is how breathable it really it - will it really allow the moisture out?

The vapour barrier on the warm side of the insulation is essential to stop interstitial condensation - a problem for heated, occupied spaces - but should that occur, it needs a way out.

Meanwhile, a breathable membrane is just to stop water penetration (rain+wind, etc), and is a second-line defence - just like roofing felt.

Remember, houses didn't include roofing felt once upon a time, and they did just fine providing no slates/tiles went missing. When our place was re-roofed by a previous owner about 20 years ago, that was the first time any sort of membrane was laid under the slates - the house would have been 100 years old at that time. All the roof timbers are in excellent condition, despite some showing water staining from previous leaks, and that's because the lack of a membrane promoted excellent ventilation - so as soon as the timbers got wet, they were able to dry out again with no lasting harm.

They fitted a breathable membrane. The surveyor didn't recognise the type, but it's a plastic weave with large-ish holes (perhaps 2mm square). It's much more breathable than any sort of building paper would be.

The loft is full of electronic debris, and has been for years, and none of it is showing signs of being kept in a damp environment despite the lack of insulation up there. Even cardboard boxes and paper/books survive unharmed. In construction terms, I regard my attic as basically a garden shed up in the air (so more exposed), but I suppose the warmth of the house must be helping to keep things dry (only 4" of fibreglass above the ceiling, and I'm quite happy about that - excess insulation makes lofts colder and more prone to problems. When/if I fit more insulation, it'll be in-between the rafters).

Anyway, all that is a long way of saying that I'm naturally cautious about adding building paper outside of the insulation, and would much rather make sure that the cladding is in good condition and everything on the cold side of the insulation is well ventilated.

Don't forget about water being trapped between the rear of the cladding and the outside of the membrane. For that reason, it's normal to add treated roofing batons to ensure an air gap between membrane and cladding, but that adds another inch to the thickness of the wall.

If I was doing a top-notch job, I'd fill the gaps between the studs entirely with insulation, then apply OSB to the outside of the studs, followed by building paper, then 1-by-2 roofing batons (in line with the studs), then the shiplap or feather-edge cladding. I'm still only half-convinced the paper is beneficial, so would do it because it probably isn't causing any harm. Probably.

Unfortunately, in the building trade, there is a lot of bad advice. Just a minute ago I saw a post on the Screwfix forum where a builder advocated putting the vapour barrier on the outside of the insulation because "that's what we've done for the last 25 years" Luckily, there's plenty of more reliable information out there for us curious engineers. For timber-framed construction, we can learn a lot from our American friends - they've got rather a lot of experience of this sort of thing. I used to watch a lot of "This Old House" and similar back in the days when I could afford a $ky subscription - of course YouTube makes this easy today.

Hope this helps,

Mark
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Old 3rd Nov 2018, 1:25 pm   #79
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Default Re: Thermal insulation for a wooden shed: advice, please.

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Which firm are you getting your timber from?

Lawrence.
Hi Lawrence.

I usually go to these people http://www.drbuildingmaterials.co.uk/timber-sheets and have been generally satisfied their timber.

Regards
Symon.
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Old 3rd Nov 2018, 1:49 pm   #80
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Default Re: Thermal insulation for a wooden shed: advice, please.

Hi

Some good points made here by Lawrence and Mark.

My original workshop, which I built exactly 27 years ago (1991) was built from sawn 50 x 50mm timber, and I can't remember if this was even treated. The stud spacings were about 15 to 16 inches so was quite a rigid structure. This had felt over it so again probably not a good idea.

I built the floor with untreated 3" x 2" timber and a 3/4" plywood floor board. I used felt under the floor joists as a damp proof (probably not a good idea in hindsight) as back in 2010 I had a look under the plywood and was horrified by what I saw. The entire chassis was rotten with white fungus all over it. Quatermass comes to mind! The timbers had the strength of cream cheese.
I should have taken the workshop down back then but managed with a great deal of effort to remove the floor chassis in stages, jacking and supporting the walls/roof etc and replaced with decent treated timbers and fitted damp proof course under the timbers. The floor looks as good as new after nearly 9 years of use so will be reusing it for the new workshop.

The roof was let down by the usual felt leaks though the original felt that I used was the heaviest one available and lasted a long time before problems showed up. I have more confidence in using something like Onduline or if the budget allows cement fibre corrugated sheets which are excellent. I like the idea of having a light coloured roof as it must help to reduce the effects of the sun's rays and keep cooler in summer. Onduline now supply grey finished bitumen corrugated sheets.

Again, that's a good point about battens over the membrane to give ventilation.

Not having any covering over the studs on the outside I'd be a little worried if there was a leak in the cladding and moisture was trapped inside and left undetected though if well ventilated should dry out fairly quickly. Heavy driving rain could be a problem though.

Regards
Symon.
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