Railway Room (External) Insulation

Not sure quite where to post this.

I have a 12 x 10 single skin (white celcon blocks on a low brick base) outside building (glorified shed actually) that was rendered originally by an ex son-in-law (begrudgingly). The rendering on parts of the builidng have been damaged this winter so some remedial work is required.

The room was built to house my model railway (never completed) and to act as a general workshop. The walls are lined inside with chipboard and have polystyrene sheeting between the walls and the sheeting. The roof is standard shed construction with plasterboard inside and filled with the same polystyrene. The floor (concrete) is made up of loft boards covered with carpeting. Prior to the boards being laid the floor was painted with bitumen. There are a couple of sealed unit windows.

From the outset the building suffered more from damp and cold over winter than I had anticipate and some form of heating was required but as costs rose, and the railway didn't progress, this had to be abandoned.

I am now trying to resurect my model railway but realise that I need to make better provision for insulation over winter. As I said, the rendering needs repair in places but would welcome any help in deciding how to make better insulation either external or internal.

Thanks

First I think you have to make good the outside rendering - either by giving it another coat (with the possibility of pebble dashing for weather resistance) and then giving it a coat of white masonry paint. However you do this, it must be completely water tight - being single skin. Were the blocks laid over a dpc to prevent damp rising? Then you have to concentrate on the insulation - which you seem to have done. However, the thicker the wall insulation the better - at the expense of losing some internal space, of course. Lag the roof space with as much rockwool as you can, but do allow ventilation into the soffits. It would also be a good idea to lift the floor and put down some closed cell foam before laying boards back down. Thats about all I can think of, anyway! Good luck with your project and hobby. Cheers John

Thanks John

Was just going to cut out the damaged rendering and make good then apply masonry paint. Can't afford to have the whole thing rendered again. The outside is already painted with masonry paint but my son-in-law gave me a tub of thick paint (Rollercoat Smooth) to paint over the rendering, which he said is like the finish applied by firms applying pebble dash finish which should make the outer finish waterproof.

Can't actually remember about the dpc but as my then son-in-law was a brickie I hope he wouldn't have missed this (hope so anyway) as it's a bit late to do anything about it now.

I can take down the internal plasterboard celing and fill with rockwool as I am aware now that the polystyrene sheeting isn't really adequate but if I do that how should I allow ventilation given that the roof is a simple shed type construction so there are no soffits.

Was thinking of fixing an inner wall to the existing using sheet ply on 2"" battens and filling the space with rockwool or similar. Did this on a garden room last year and it worked fine.

Not heard of closed cell foam but this seems a good idea, is it available from normal builders merchants or DIY outlets and any idea of cost?

Chris

Hello Chris
Making good the original rendering is a sound idea - just make sure it hasn't 'blown' away from the blockwork which will give problems later. Masonry paint is about as good as it gets if you don't want to pebbledash.
Regarding the ceiling and roof void, if you take the ceiling back down you could pack rockwool or similar between the rafters before putting things back again. You do need to get some ventilation into the still air space in the roof void somehow - maybe this could be done by using screened ventilators in the gable ends it it has them (pitched roof) or through the facias if its a lean to type.
If you are replacing the ceiling with plasterboard, you could also cover that with particle board (which is similar to the material used for facing notice boards that you can stick pins in) but there could be an increased fire risk here.
Putting up extra studding for the internal walls is a good idea too - you can use slab insulation for this which makes things a bit easier.
For the floor, a closed cell foam such as polystyrene slab is easy to get from Wickes etc and so long as it can't absorb moisture, and re-lay the floating floor on top.
If the roof has corrugated panels you can fill any gaps with expanding polyurethane foam - this stuff is useful for filling any gaps anyway.
Hope this helps!
Cheers John

Hi John

Think the rendering has "blown" in a couple of places. The wall is question is very open to the elements and as I live in the country the wind etc. coming off the field at the back has probably been the cause. Was going to cut it back, apply pva, and then patch, that's just about within my limits on rendering/platering.

Could probably fit a screen ventilator in the roof gables, will need to check as it's not much of a pitch or see if there is an alternative I can adopt.

Wondered if I could replace the plasterboard on the celing with mdf board as it will probably get damaged when taken down. Again have used that in the garden room and it worked well over it's first winter. Could possibly use that too for the inner skins as I think it would be a bit cheaper than ply.

Will take a gander in Wickes and see what they have to offer for the floor, don't want to put down anything too thick of course. Don't think there is any damp coming through as I haven't noticed it on the carpet. Had a couple of mouldy sections in the corners a couple of years back but think that was because I had things stacked inhibiting air flow.

Chris

MDF is fine for a plasterboard replacement - ply may be even better as its stronger and the external grade has good moisture resistance. Obviously neither has the fire resistance of plasterboard but this doesn't seem to be an issue. You can also fit 'slate ventilators' into the roof shell itself - it depends on how far you want to go, and whether you have a felt covering or shingles, slates etc. Look at Screwfix part number 43099 for these.
Enjoy the project!
Cheers John

Without heating you are on a hiding to nowhere! Sounds like your ex-brother inlaw had some sound idea's although maybe a bit lacking in technical knowledge.

First point, external render failure is down to 'frost attack' due to the walls being so damp in winter - cause interstitial condensation, situation may have been eased if you had some heating in place.
2nd point - installation detail of insulation maybe wrong, if the insulation is touching the external wall then this will only worsen the interstitial condensation problem on the outside wall, and if the insulation is relatively thin say less than 50mm and is jammed between the wall and the internal boarding you will be getting thermal bridging which will cause surface condensation to occur on the inside of the building, regardless of the fact that you may have installed a vapour barrier (works two ways keeps vapour out but can also keep vapour in).
3rd point - if there is no cavity (need only be 25mm but ideally 50mm) then external condensation point will be between the insulation and the external wall thereby making matters worse. With a cavity the condensation point would most likely be on the internal face of the external brickwork - the ventilated cavity would then allow the condensation to dry out, rather than saturate the brickwork.

Solution to your problem - strip out all the existing insulation (ceiling and walls), leave a ventilated cavity and roof void and install a proprietary urethane insulated plasterboard minimum insulation thickness 50mm ideally 80mm (this should then make the building economical to heat!) directly to the existing timber studs/roof joists which will then give you your cavity. As said before without heating you are on a hiding to nowhere!
By keeping the area relatively warm to the outside temperature (use a frost stat in your heating system) you will avoid any surface or interstitial condensation forming within the building, urethane being vapour resistant also gets over the problem of having to install a vapour barrier, any condensation that does occur will happen in the ventilated cavity, and should no longer be a point of concern. As for the floor, a single skin of brickwork was never going to stop rainwater penetration and you may want to consider a raised floor with cross ventilation and fit insulation between joists, you can purchase a net that sits over the joists and keeps the insulation in place.

Once you have got these issues resolved, you will then be in a position to consider tackling the external repairs.

Regards

alittlerespect

Thanks for your detailed reply. Wanted to check I have understood what you are saying before I start working out an order.

If I replace all the internal wooden wall panel with urethane insulated plasterboard (50mm or 80mm) using the existing battens which from memory will I think provide a 25mm(1") cavity this will be sufficient? I could of course increase the cavity by fixing another 25mm batten on top of the existing without too much trouble thus doubling the cavity if this would make a significant improvement.

A friend has suggested putting a membrane between the battens and the plasterboard. Is this a good idea?

Similarly with the roof area, I can remove the exiting plasterboard and again replace with urethane insulated plasterboard and leave the roof area clear (why no insulation as with a normal house loft area). Does the roof need any ventilation? Have taken a quick look and I think there is only about 3 inches space between the ceiling board and the apex of the gable end (it was as I said built on shed lines and the roof pitch is very shallow) so not sure I could fit screened ventilators as suggested by Burnerman. The roof is therefore normal boards covered with roofing felt so not sure how I could fit any ventilation in the actual roof.

As for the floor. From memory I bitumed the concrete floor, laid 3" x 2" cross members and then laid the floor panels on that, so the floor is slightly raised and has a void underneath, not got any insulation in the void.

Finally heating. When I did heat the room I used oil filled radiators that had their own thermostats backed up by an electric fan heater. These work out fairly expensive if running 24 hours a day, especially in todays higher fuel cost. Probably a halogen heater would be cheaper than a fan.

You mention using a frost stat but this wouldn't work with electric radiators I have. Wondered what the minimal heating I would need to keep the room dry and keep costs down. I have seen the long electric tube type heaters you see in portacabin toilets and these could be wired into a frost stat to come on during cold spells with additional heating as and when required if I am working in the room.

Wondered if this would be sufficient or is there a better method I could use? Always bearing in mind the running cost factor.

Should mention that one of the benefits of using chipboarding on the walls is that hooks and other fixings can be done easily and wherever I want them. If I were to refit the boards over the top of the plasterboard, or even mdf, would this have any detrimental or beneficial effect.

Thanks

Just wanted to update on progress.

Have removed all the wall and ceiling panels and removed the polystyrene insulation. Can now see that there are six courses of brick beneath the blocks. I remember painting the first 2 courses and the floor with bitumen paint.

There has been some damp in the corners and think some of this this is likely to have been due to a log store we had along one outside wall. There is no evidence of damp on the floor and I am now certain that the floor is suspended on 3" nominal bearers.

The battens for the wall panels are as I thought 1" nominal after fixing the new wall panels this will leave a 1" cavity.

Due to the construction of the building I can only fit a 25-30mm board (inclusive of insulation) on the ceiling otherwise it will foul the door. Fitting 50mm or 80mm on the walls is no problem.

Think I can fit a screened ventilator in the gable ends.

Is there anything else I need to take into account before I go out and order (see my previous questions).

Thanks for the update, Chris.
I think that alittlerespect and I are on the same side of the fence here - he very rightly so talks about a building in an ideal situation and of correct construction - which is rather a long way away from yours!
However, if you can follow the advice given as far as possible you'll get a job as good as it can be. So- to recap:
1) Leave an air gap between the outer wall if you can, but the greater amount of insulation you can install between outer leaf and inner the better. Consider - outer wall, air gap, insulation, vapour barrier then internal wall board. If you can ventilate the air gap with a type of air brick or similar, so much the better.
2) Insulate below the floor boarding with expanded polystyrene foam, which can't absorb moisture.
3) Insulate above the ceiling as much as you can, but try not to let the insulation touch the roof shell.
4) Ventilate the roof void if possible.
5) Ensure that the building outer shell is as water tight as can be - avoid deposits of soil etc from touching the outer blockwork.
6) On the inside, avoid furniture etc from touching the inner wall - leave an air gap.
7) Regarding heating - remember that insulation alone does not make a building warm - it only conserves whatever heat that you may put in. Tube heaters have their place, but as they only consume about 100w at best its only the same as a light bulb so you can't expect to be cosy with these - they are really only designed to prevent pipes freezing by keeping the temperature above 0 deg.
Please don't think I am trying to be patronising with what I have said - only trying to help etc - and best wishes with the project. Would like to hear how things go!
Cheers John

Thanks Burnerman all points appreciated.

Will try and follow the advice to the best of my ability but as you rightly say I have to work with what I have and therefore some compromise is inevitable (due to cost) and it is after all a model railway room not living accomodation

As regards heating, wasn't proposing to use the tube heaters as the main source just to keep the building at above freezing when I'm not actually in the room or overnight.

As regards avoiding furniture touching the inside wall. This could be a problem as the the new railway layout I am obtaining would I think need to be fixed to the inner wall via battens on one side. Currently it is in a 8 x 6 shed and is fixed to both walls with a walkway in the centre. Will need to see the actual construction when i get it home to see how it needs to be anchored.

Is it essential I have insulation in the roof void if I use say 25mm insulated plasterboard on the ceiling.

Will try and source what I want today and will certainly post back once I have finished, as it may help others with similar problems.

I think the insulated plaster board will be as good as it gets, regarding the limited space available up there.....so go with your proposals and see how satisfactory it is.
If its freezing then you'll just have to turn the heaters up!
Cheers John

Hi John

Sorry to come back so soon but have been ringing around for prices on insulated plasterboard and getting a nasty shock with prices of between £30 and £35 per 50mm sheet being quoted.

Spoke to BMD Insulation online and they suggested that instead of bonded insulation/plaster board a more cost effective way (about half the cost) would be to buy the insulation sheet and plasterboard separately.

Given that this is just a model railway room £30-£35 per sheet is really excessive. Told by BMD that the two separate sheets would give the same insulation properties for what I want once fitted.

Was also wondering about fixing, especially on the ceiling, presumably drywall screws would be OK. The wall boards would be 50+12.5mm so would need long screws, assume these are readily available?

Any comments

Chris

Hi Chris
I can't really comment on the prices of the insulated plasterboard, but I'd be inclined, as you seem to be, to manufacture my own, using sheet insulation of some description with the plasterboard beneath, holding it up.
Dry wall screws will be fine, and you have a choice between the black phosphated ones and zinc finish. The proper ones have bugle heads to prevent tearing the paper, and allows them to be easily set to the correct depth. Screwfix do 4.2mm x 75mm long - part number 18586 - in 500 packs for £7.53.
You'll need a helper to hold the sheets up as you fix them!
Cheers
John

Thanks John, this looks the most cost effective way to proceed.

Yes I have a "willing" helper. Have a team of three Bodget The Builders, all retired and our motto is "We have the will but not the skill".

Cheers

Chris