Is this sensible?

[SammyQ]

I'm shamelessly aiming this at MikeG. - and any other architects or knowledgeable builders hereon - if he or they want to fulminate and castigate me for shameless cadging (consultation in sheeps' clothing?), please feel free; I'm operating on the principle 'you can only ask, even if you get turned down'...

Scenario: I am 62, a retired teacher, with that profession's pension as my sole income for the next four years. I have just moved/downsized house, to N.E. England , just above Newcastle. It has a detached sectional concrete garage, 16' x 8' in old money, with a pitched, corrugated concrete roof, looking suspiciously like asbestos sheeting. I want to line/insulate the beast to have a proper workshop for the first time in my life, but keeping fiscal outlay to an absolute minimum and physical labour similarly minimal, for other reasons. I have several vulnerable machines: a Wadkin AGS, a Crescent-clone bandsaw, planer/thicknesser, two dust extractors, a gurt big floor drill and numerous (but enough Mike!) hand tools all vulnerable to tinworm in the presently damp conditions in there. It's condensation for sure, for sure, brought on by weather change and my heavy breathing... on the (now) cold under-surface of the roof. Floor, walls and ceiling are all sealed, including gaps under corrugation 'peaks'; don't know that they could be called "eaves"?

Query: I've read oodles online about the dire potentials of asbestos roofing. But...mine isn't leaking and appears to be in good nick (photos later)...is there any GOOD, SCIENTIFICALLY VALID reason for not simply leaving it alone and sealing its underside - i.e. my proposed workshop ceiling? That would negate dust falling from its underside and giving me mesothelioma or worse. I'm thinking cellulite...sorry, Celotex, or similar; wedged, glued, SEALED, tight up against the lower surface of the corrugated material of the roof. This, I naively believe, might be called a 'warm roof'?? I reckon the foil backing would also count as an impervious layer? As, of course, would the expanded foam? I do not presently see any need to open up the sealed edges at the wall-roof junction, as I believe there is no need for air circulation in said 'warm roof'?

I also intend to smooth the rough concrete floor, then DPM it, batten out with metric 2" by 1" rough, 50mm Jablite/Celotex into the voids and lay a loose (floating) floor with 18mm T&G boarding, glued together on the joins. The THIN horizontal pre-cast sectional walls I propose to 'dot and dab' 50mm Celotex to, resting it on the flooring, left naked, save where I need to over-board with solid ply or other boarding to hang tools on etc. For that, I'll add floor to ceiling battens, to transfer load to the floor, rather than risk 'pullout' from the (apparently) 25-30mm panel thickness of the walls.

Sorry I have no photos presently, they are locked away in the attic on my PC while we complete work in the house. I will add phone photos, upon request, for clarification, if needed.

Have at it Lads...

Sam

 

[Marineboy]

I can’t offer advice a la Mike G but just wanted to say welcome to the NE. I’m in Blyth, Northumberland, a great place to be.

 

[SammyQ]

Thanks MB. Alnwick here.

Sam

 

[Marineboy]

Posher than Blyth.

 

[Spence]

I am not an expert in Asbestos, but my gut says leave it alone if you aren't going to pay someone to remove the stuff. If its undamaged and you don't plan on damaging it by drilling into it or cutting it in some way leave it alone. I'd pay and have it removed, better to do that now before you have it all finished inside.

Does this outbuilding have a damp proof course? It might be hard to see the signs but worth looking for. I'd agree with insulating the floor, I've just come from a workshop that has a bare concrete floor and that was incredibly cold to work on during the winter.

Pictures would be great, I do love a shed

 

[MikeG.]

Who, me? :lol:

 

[MikeG.]

Firstly, Sam, what you are proposing is not a warm roof. In a warm roof, the roof structure (rafters, purlins, joists etc) is underneath the insulation, and so within the insulated and heated space of the building.

Secondly, your proposal would create unventilated voids above the insulation, full of air with fluctuating temperature, and thus certain to produce condensation, which you have now trapped above insulation. This will then run down the top of the insulation/ underside of the roofing material, and sit on top of the wall, doing all sorts of harm including growing unhealthy mould.

The good news is that if your corrugated roof sheets are in good order they are perfectly safe left alone (and as an aside, mesothelioma has an incubation period of 30 to 40 years, so unless you were planning to live to be 100+ you shouldn't worry about it too much anyway). The other good news is that there are a number of good ways of insulating your roof such that you'll be warm and your tools safe from rust. The design of these is going to depend on how you want to get airflow in under your roof sheet, because that is certainly what you'll need to do.

The simplest way is to insert a ceiling at wall plate level (ie top of the walls), and insulate on top of it. This will mean spanning across with timbers (5x2s at 600 centres if you don't want to store anything much up there), putting in a ceiling of moisture-resistant material such as OSB or foil backed plasterboard, and then you can use the much cheaper fibreglass insulation and just pile it in. Ventilation by means of a big grill/ vent in each gable is dead easy.

The more complex answer is to insulate underneath the roof sheet, giving you greater headroom but greater headaches. Here, you would need to space the Celotex at least 25mm and ideally 50mm down from the underside of the "valleys" in the roof sheet, which is going to involve some structure, then open up all the blocked up airways at the eaves. Not only that, but you'll have to insect-proof those openings otherwise you'll create a haven for wasps, birds and even rats. You'll still need a ceiling below the insulation, mainly as a vapour barrier (again, OSB or foil-backed plasterboard).

There are other more exotic and expensive answers, but those are the 2 fundamental choices for the DIYer.

 

[paulrockliffe]

It also won't be a warm roof if there's no heat source. All the insulation will do is stop it going cold quite as quick when winter turns if there's no way to heat it, so make sure you sort that too.

 

[MikeG.]

Your solution for the walls is OK*, but you must be careful to eliminate voids. If going down that route I would suggest spray-foam adhesive for gluing the Celotex to the concrete panels, and to run continuous beads rather than dabs.

Why are you wanting to put battens in the floor? You'll be fine (on a flat substrate) with just a T&G board on Celotex, although you should use 22mm chipboard rather than 18 in light of your machinery. The one complication is that a floating floor works by being trapped down at the edges by the skirting board, and your proposed wall doesn't give you anything substantial to fix a skirting board to. *I personally would be using 2x2 battens down the walls with Celotex between, OSB over that, as that would give me something solid to screw skirting to as well as providing walls capable of supporting shelves, racks, tool cupboards etc.

 

[SammyQ]

Mike, thank you heartily for the clarity and the detail of your answers. And secondly, for taking such a long time out of your busy, productive, days to provide guidance. I will reflect on things and adapt my plans accordingly.
I had considered opening up the blocked corrugations atop the wall, but was seduced by the thought that leaving them alone reduced labour. Laziness in a different coat I guess.
The battens on the floor were because the concrete floor was very roughly tamped and badly levelled. I need to eliminate a disparity of maybe 1-2 cm over a distance of 1-2m and this is repeated transversely as well as longitudinally, throughout the floor. Real urine hindquarters of a job.

My fervent thanks again, will let you and fellow forumites know how it pans out. Mind you, Mission Control is making portentous noises re Christmas preparations. Watch this space.

Sam.

 

[beech1948]

This is not an answer to SammyQ's questions but an extra query. The asbestos cement roof if solid should be OK so is it possible to create an insulated roof over the asbestos cement and not under it.

This could be self ventilated and self draining. Just an idea but once asbestos cement is fully encapsulated ( eg with a coat or two of paint) then the extra headroom would be worth it maybe.

 

[MikeG.]

Mike, thank you heartily for the clarity and the detail of your answers. And secondly, for taking such a long time out of your busy, productive, days to provide guidance...........

Payment, as always, is by way of photos posted of the project as it develops. The more people do that, the less I have to type!

 

[MikeG.]

This is not an answer to SammyQ's questions but an extra query. The asbestos cement roof if solid should be OK so is it possible to create an insulated roof over the asbestos cement and not under it.

This could be self ventilated and self draining. Just an idea but once asbestos cement is fully encapsulated ( eg with a coat or two of paint) then the extra headroom would be worth it maybe.

It's really difficult to see how you could build a roof without access to the wall plate or fixing through the asbestos, and in both instances you would be disturbing the asbestos and thereby creating a hazard. Whilst it isn't impossible this could work in specific circumstances, I can't picture it. I'd never advocate anything other than extreme caution with disturbing any form of asbestos.

 

[SammyQ]

Pictures. Understood.

S.

 

[bourbon]

I'll throw a spanner in the works here. Is there an impressed number on a corner of a sheet? The reason I ask. I work in a place that had sheets covering an out building, There was a big uproar (Quite rightly) that they were asbestos. The company had loads of tests done at vast expense. I merely noted the numbers printed on each sheet and spent an evening exploring the internet. The results of the tests came back, to which I replied 'yes I knew what they were three weeks ago!' They were concrete with no asbestos used at all.

 

[SammyQ]

Bourbon, you are a star. I followed your lead online and will be out in the morning to peer at corners. If we have concrete sheeting ' Job's a good'un'. If not, scheme on.
Sam

 

[SammyQ]

Just quickly re-reading this and noting down ideas/details over breakfast..noticed "urine hindquarters" ... ($%~~ing auto correct!); make that "ursine hindquarters"...'bear's arris'?

Always a pedant, Sam

 

[MikeG.]

No, Sammy, the roof sheeting material makes no difference to the insulation and construction details I outlined. Unless, of course, you are proposing taking the sheets off and building a new roof.

 

[SammyQ]

Understood. Ramifications extend in a different way, will send a (brief!) PM to explain.

Sam

 

[Tervueren]

At my previous home I had a prefab garage and it was a nightmare, I'd swear it was colder inside than out lol, the concrete walls streamed condensation and the roof supplied plenty of ventilation when it was windy !! Mine was used just as a garage with minor storage of bits n pieces, after throwing away lots of stuff ruined by the damp I decided to do something about it. I removed all the "asbestolux" roofing sheets and put a flat roof on it using 6x2 with firings to provide enough fall, then it was a simple fibreglass insulation above the plasterboard ceiling, the walls were battened and covered with Rockwell and finally polystyrene backed plasterboard, after doing all of this it was still bloody cold in there but it did help with the condensation problem but without auxiliary heating was definitely a no work area in the winter lol