Advice needed on insulating external walls

jennifernil

Not in my  home, however, but in our local Girl Guide hall which I help to look after.   Some background......

The building is from 1961, a brick + block built basement used only for storage, supporting the main building which is timber frame with horizontal timber T&G cladding on the  outside and plasterboard of unknown thickness inside.  The timber frame is made up of 4"x2"  timbers, I have the original building plans as submitted to the local council.  We believe there is possibly 2" of glass fibre insulation in the walls somewhere, but quite likely that this has "slumped".

The  main area of the building under consideration is approx 10m x 20m, there are additional rooms at the back, but insulation in these has already been improved when modernisation was done.

The floor is hardwood T&G planks, uninsulated we believe,  but we can deal with that later.  The roof was replaced about 20 years back and is steel sheet with Kingspan type insulation, plasterboard ceiling, so we are happy with that.   It is a mono-pitch roof with the internal ceiling following the roof line, so high at the front both inside and outside.

We have double glazed windows and insulated doors, all less than 15 years old, and a gas central heating  system with condensing boilers less than 5 years old.

Most of the time it is warm enough, and we are meantime on a fixed tariff for both gas and electricity for another year, but we are very worried about future fuel prices.  In the recent  very cold spell, even with the heating going  flat out, an acceptable temperature in our 2 main front halls could not be reached, and some activities had to be cancelled.

We obviously need to insulate the walls, but what is the best method?

Removing the T&G cladding to do it from outside would likely result in needing all, or a lot of, new timber, which is expensive these days, and as the building is at an upper level relative to the parking area, a lot of scaffolding would be required.  However the disruption to activities would be minimal.  However I do not know whether that would give easy access to where the insulation should be placed.

Removing all the internal plasterboard, skirtings, window finishes, radiators etc etc to do the work from inside would be extremely messy and very disruptive, meetings would need to be cancelled for several weeks.

 Both these options would be possibly more expensive than our emergency fund could cover, though we have not yet got any quotes

Before I start looking for quotes, are there any sensible alternatives we should  consider ?

Norman_Castle

I'd start with a thermal camera to find out how bad the walls are. If there are cold spots could these be repaired through small cut outs through the plasterboard?  I've insulated under a floor by only removing 1/5 of the floorboards and reaching under the others.

Definitely check for draughts, they'll be the easiest and cheapest to resolve. Check where pipes go through walls and floors including behind or under cupboards and check where the skirting meets the floor. You can buy foam designed to fill these gaps which is very easy to fit. Get the guides to do it to save your knees. As there's a basement does that give access to the underside of the floor?

FreeBear

jennifernil said: We obviously need to insulate the walls, but what is the best method?

Removing the T&G cladding to do it from outside would likely result in needing all, or a lot of, new timber, which is expensive these days, and as the building is at an upper level relative to the parking area, a lot of scaffolding would be required.  However the disruption to activities would be minimal.  However I do not know whether that would give easy access to where the insulation should be placed.

Removing all the internal plasterboard, skirtings, window finishes, radiators etc etc to do the work from inside would be extremely messy and very disruptive, meetings would need to be cancelled for several weeks.

Third option is blown insulation. Either fibreglass/rockwool or polystyrene beads.

But you really need a detailed assessment of the wall construction beyond what is mentioned in the plans. Questions that needs answering -

• Is there a membrane behind the timber cladding ?
• If there is a membrane, is it bitumastic felt or a breathable one ?
• Any vapour control membrane underneath the internal plasterboard ?

Once you have answers to the questions, you will be in a better position to make an informed decision about which method would be best within the budget.

ThisIsWeird

I think the easiest and least disruptive method would be to add insulated plasterboard to the inner walls. That should be a very quick process - glue and screw the boards in place, and either plaster skim or tape-and-fill the joints. Coat of paint. Done. (Except skirtings, rads and sockets would need removing and refitting...) This should also be supremely effective - a, say, 2" layer of Celotex-type insulation enveloping the room should transform its insulation value - it would be effective even if just on its own, but all the existing insulation value in the wall will be contributing further.

Main drawback would be the 2"+ loss of internal space each side, but that doesn't seem a biggie.

All other methods will be quite destructive, messy, and a lot more labour-intensive as they'd involve first removing either the inside or outside wall fabric. And there is no certainty that the insulation value could be made better than with this simple overlay on the inside.

I am not saying that to first gain access to the wall core and try and add insulation that way might not have some advantages, but I can't really think of any; it would surely be more costly, take longer, and very likely be less effective, afaIcs.

Any chance of a pic of the plans to show the wall construction?

Apodemus

Another vote for an additional layer of insulated plasterboard as the least disruptive and cheapest option.  Not the best solution or the most elegant, but it will work!

Incidentally, at that age, the glassfibre insulation may be an older type where it is literally glass fibres contained between two paper layers.  Horrible stuff to remove or work around, but doesn't seem to slump and is more resistant to getting damp. 

ThisIsWeird

Apodemus said:
 Not the best solution or the most elegant, but it will work!

I don't understand this bit. It will surely provide perfect inside walls?

ThisIsWeird

If the hall takes some bashing, then an alternative could be the 2" (or more) layer of Celotex, covered by wallboards - not even plastering and painting required. 

(All these solutions would need to be fire-assessed, of course.)

I help out at a similar hall here - ex temporary classroom buildings - and the lower roughly-half sections of the walls are panelled to take the knocks. So only the exposed p'board joints above this would need filling and sanding for paint.

jennifernil

Thanks for the input so far!   

 I will dig out the plans I know I have somewhere and see if they give any more details on the wall construction.

Insulated  plasterboard added inside the existing had come to mind, and I also asked the builders who were working on our bathroom recently and they suggested a layer of the thickest double bubble foil stuff over existing, then strapping and new plasterboard over.

Finding it difficult to work out just how much this would improve things in a way we can understand.

These solutions would certainly be less messy and  disruptive, but maybe not entirely straight forward.     Preparing the internal walls will involve removing all the old skirtings, 8 huge radiators, 10 large pinboards, several large cupboards, 12 curtain rails and all the facings round the 12 windows.

All this would have to be replaced afterwards, plus the window reveals and sills,  which are presently not deep, would need to be extended to cover the increased depth before the facings are replaced.

Wall heights are about 3 metres at the lowest point sloping up to maybe 6 metres at the highest  .........really need to dig out those plans.......so a lot of wall to cover!

Will come back once I have more detailed information.

 Meantime I will look into whether there is any help with the cost available.

FreeBear

ThisIsWeird said: (All these solutions would need to be fire-assessed, of course.)

In light of this being a public space and with Grenfell in mind, polystyrene & PUR/PIR might not be the best materials to use. Cork would be an excellent insulator with very good fire resistance, but it is expensive.

As the work involves more than 25% of the building envelope, Building Control would/should be involved - They will have final say over what materials can be used.

ThisIsWeird

jennifernil said:

Thanks for the input so far!   

 I will dig out the plans I know I have somewhere and see if they give any more details on the wall construction.

Insulated  plasterboard added inside the existing had come to mind, and I also asked the builders who were working on our bathroom recently and they suggested a layer of the thickest double bubble foil stuff over existing, then strapping and new plasterboard over.

Finding it difficult to work out just how much this would improve things in a way we can understand.

These solutions would certainly be less messy and  disruptive, but maybe not entirely straight forward.     Preparing the internal walls will involve removing all the old skirtings, 8 huge radiators, 10 large pinboards, several large cupboards, 12 curtain rails and all the facings round the 12 windows.

All this would have to be replaced afterwards, plus the window reveals and sills,  which are presently not deep, would need to be extended to cover the increased depth before the facings are replaced.

Wall heights are about 3 metres at the lowest point sloping up to maybe 6 metres at the highest  .........really need to dig out those plans.......so a lot of wall to cover!

Will come back once I have more detailed information.

 Meantime I will look into whether there is any help with the cost available.

Blimey - I suspect the sheer open volume of heated space up above their heads will be a large reason why it's so hard to heat. I bet a suspended, insulated ceiling set at the lower 3m height (or even slightly below) would transform the ability to heat that hall?

Norman_Castle

Would they benefit from one of these? https://www.flexiheatuk.com/product/destratification-fans/