Pre-fab Concrete Garage - Ventilation

[woodyfox]

Hi all,

 

It appears that a new project for 2019 will be the conversion of a pre-fab concrete garage with pitched, corrugated asbestos roof into an insulated space for a railway project. I've done some research into the way to achieve a decent room but one question remains. Is there a requirement for some level of ventilation to and from the insulated room? I assume something airtight is as bad as mixing cold and warm moist air? Has anyone any experience of such a project? I'll be insulating the floor, walls and putting in a false ceiling using king span in between batons overlaid with OSB board.

 

The resulting usable space will be around 16 feet by 12 feet.

 

Thanks in anticipation.

[chris p bacon]

The best way to ventilate a pre-fab concrete garage is to flatten it. . . 

 

They're fine for the purpose of overnighting a car to keep the worst of the weather off, but I wouldn't recommend them for anything else.

[woodyfox]

The best way to ventilate a pre-fab concrete garage is to flatten it. . . 

 

They're fine for the purpose of overnighting a car to keep the worst of the weather off, but I wouldn't recommend them for anything else.

Hi Chris. Thanks for your reply. A substantial body of evidence exists that suggests this type of building is entirely convertible. Your assertion suggests you have a personal experience. Would you be able to expand upon your assertion and provide a reasoning for such a view?

 

Thanks

[chris p bacon]

I've put them up and taken them down.

 

I'm sure there's some examples of people making a decent job of them, but I've always found them to be prone to condensation and requiring major works to provide a reasonable amount of insulation.  One issue has always been the internal height. For a garage it is sufficient, but adding insulation to the ceiling and floor reduces the internal height to barely 6'.

 

They are usually on a decent concrete base so I have suggested in the past taking the old garage down and building a timber framed building in its place, I'd be tempted to say that the cost would be comparable allowing for the superior conditions within the wooden building. 

[TheSignalEngineer]

We tried using them as lineside equipment huts about 50 years ago, absolute disaster. Even when containing several transformers and a few dozen relays they needed extra heat 24/7 in winter to stop condensation. They were a worse environment for equipment than a steel cupboard.

 

Changed to prefabricated ones made from polyurethane foam sandwiched between coated steel sheets. The only problem with those was they were too well insulated and got too hot in the summer.

[N15class]

What ever you decide to you need to put a barrier between the concrete and the wood and kingspan. To stop the air condensing on the insulation. Trying to waterproof and insulate an existing structure is a nightmare. The smallest gap or break in the WPM will waste all the good work. Building new with the WPMs in the right place is the best way to go.

As above you are going to reduce the size internally quite considerably. Last time I did insulation with kingspan or similar. I think it was 150mm on ceiling 100mm on floor and 75mm walls then there is the extra thickness of whatever you use as a lining and floor. The ceiling would need to be under the steel trusses, or they would bridge the insulation. I think or pre fab was 6'6"to truss. So by the time you've blinded the floor to stop the membrane puncturing put a floor over the insulation. You will of taken 11 to 12 inches out of the 6'6".

[Richard_A]

How about externally cladding with a phenolic insulation and rendering the walls, and installing a warm roof over the existing one?

[PhilJ W]

Whatever you do that asbestos roof will be a problem. As Chris said, flatten it and build something more suitable in its place.

[cypherman]

Hi all,

As said the roof needs to removed by a specialist company. That will be expensive. I am not sure but it may also be a legal requirement to have it disposed of if you are doing any structural work on it, Especially if any one else is to go into or use that building. It is something you really need to look into. Your local council will probably be the best place to start. You could also make sure it is asbestos and not just preformed concrete panels.

Edited September 25, 2018 by cypherman

[polybear]

Some councils will dispose of Asbestos free of charge as it's cheaper than cleaning up fly tipped material.  I see no reason to employ a specialist firm to remove it as you're not cutting or drilling it.  Many places will accept it so long as it's double wrapped in thick polythene etc.  On my shed the asbestos roof seemed to become porous and leaked water; roof sealant worked for a while but wasn't the answer.  The cost for specialist disposal (with me removing it) was silly money; in the end I re-roofed it using galvanised box section sheets with battens on top and the asbestos laid and secured on top of that.  Worked a treat.

[N15class]

The asbestos in corrugated is not the harmful one the lagging which I do believe was the brown is the nasty stuff, but it's not good to saw or drill as any dust is bad for you. It as said be accepted by councils if properly bagged. How old is the garage as if it less than 30 to 40 years it will probably be fibre cement sheets.

[The Johnster]

You can seal the asbestos with a 50/50 mix of pva and paint.  But you'll need to thoroughly clean it of algae and stuff on the outside first, and it will not be able to bear your weight without crawling ladders; use a face mask while you are cleaning it and pick a damp day.  As Peter says, the asbestos is not the very harmful brown, blue, or white stuff but this does not mean that you should expose yourself to breathing it, just that you don't need to be wearing a full NBC suit with a filtered face mask.  We are not clearing up after the Roswell crash here...

 

If it is removed, it has to be bagged in asbestos rated bags and disposed of in a location licensed for it; this will cost a bit!   It might be that the best way forward is to demolish it and build a new one with less problematical materials.

Edited September 25, 2018 by The Johnster

[Damo666]

Some councils will dispose of Asbestos free of charge as it's cheaper than cleaning up fly tipped material.  I see no reason to employ a specialist firm to remove it as you're not cutting or drilling it.  Many places will accept it so long as it's double wrapped in thick polythene etc.  On my shed the asbestos roof seemed to become porous and leaked water; roof sealant worked for a while but wasn't the answer.  The cost for specialist disposal (with me removing it) was silly money; in the end I re-roofed it using galvanised box section sheets with battens on top and the asbestos laid and secured on top of that.  Worked a treat.

Need to be very careful on the removal of asbestos, it's normally a licensed requirement. Where a license is not required there are strict requirements, for the protection of the worker and the public.

 

See the full document, here's an extract (I haven't read it myself, I usually rely on our CDM planning supervisor to know what needs to be done on our sites):

 

Examples of non-licensed work with asbestos

• Cleaning up small quantities of loose/ fine debris containing Asbestos Containing Material (ACM) dust (where the work is sporadic and of low intensity, the control limit will not be exceeded and it is short duration work)
• Drilling of textured decorative coatings for installation of fixtures/fittings
• Encapsulation and sealing-in work on asbestos-containing materials (ACMs) that are in good condition

Removal of:

• asbestos cement products, (eg roof sheeting and rainwater goods) provided the material is carefully handled/removed without breaking up; this includes work with asbestos cement which is weathered but not otherwise substantially damaged

Risk assessment

All non-licensed and notifiable non-licensed work with asbestos needs a risk assessment and must be carried out with the appropriate controls in place, and those carrying out the work must have had the correct level of  information, instruction and training, to protect themselves (and others in the area) from the risks to health that exposure to asbestos causes.

Edited September 25, 2018 by Damo666

[chris p bacon]

We have had the white cement board before (it's not really asbestos, that's the fire proof lagging) The advice was that so long as it stayed on site it wasn't a problem, it was only if it needed to be removed did it have to be wrapped and collected by a licensed carrier.

On the several occasions we dealt with it, it became part of the hardcore or was put in the soakaway, always with the knowledge of the Building Inspector.

[woodyfox]

Hi,

 

Thanks for the responses. The roof is not just asbestos but the cement sheet stuff. The structure has actually been quite well maintained and is dry and well ventilated as it stands.

 

Thanks once again.

[chris p bacon]

I just found a pricing sheet from 4 years ago where I was asked to give a costing on materials for a large lodge/wooden building.  It was compared to a static van so was based on 30'x10' with simple base and felt (torch on) roof, fully insulated and finished in shiplap board with an allowance for bath & kitchen it was £7,800 for materials and some specialist labour.

Just checking it over and removing the items not required for a railway shed and reducing it's size to 20' x 10' brings the costs down to sub £5000, sounds a lot but it was quoted as a habitable building for occupation. Changing some of the material spec and it would be possible to bring the cost down another 25-30%

[Nick C]

Our local council will take up to 15 sheets of asbestos at the tip, but they charge £12 per sheet...

 

A friend of mine once dismantled an asbestos garage, but his council only allowed 6 sheets per person. So he took 6, then his wife took 6, then his dad took 6...

 

I'd go with Dave's suggestion - a purpose built timber-framed building would be much better. If you're capable of building it yourself you can get them in kit form too, which might reduce the cost further? Or even scratchbuild!

[Harlequin]

Relating to ventilation: If you insulate inside an exposed concrete structure the dew point (the position on the temperature gradient from inside to outside where any moisture in the air condenses) will almost certainly be inside the insulation or possibly on the surface of the covering board. This can cause some types of insulation to degrade, timber to swell and rot if not treated, fixings to rust and electrics to get damp. If so, it might be difficult to make the inside space "livable" in the winter while also having sufficient ventilation to avoid the damp problem.

 

If you could insulate outside the concrete panels, add a moisture barrier, air gap and rain screen (e.g. shiplap) that might be a better way to use the existing walls. You'd need to get someone properly qualified to work out the exact build-up. But maybe that's not practical and it's probably approaching the amount of work to knock it down and start again!

Edited September 26, 2018 by Harlequin

[N15class]

Hi,

Thanks for the responses. The roof is not just asbestos but the cement sheet stuff. The structure has actually been quite well maintained and is dry and well ventilated as it stands.

Thanks once again.

There is a big difference between it not being wet and being dry. The concrete base will probably not have a DPM so will always be damp. Both the concrete sides and the cement/asbestos roof will both be damp. Concrete is not waterproof.

While it is not sealed it looks to all tense and purpose to be dry. As soon as you insulate and stop the air flow, it will all show its ugly head.