Vapour Barrier or no Vapour Barrier

[teddy_amok]

Hello, I hope you are all well <3

 

I live in a very old sold wall granite building (approx. 100 year old). The building has 2 floors and a small loft. The bottom floor is owned by a property leasing company and me and the wife are on the 2nd floor.

The building has a solid granite wall exterior, a gap (which runs from sides of walls into loft), and then plaster boarded interior walls. We have no central heating. As you can imagine, the flat is cold.

 

The loft had badly laid fibreglass insulation. This had been compromised and ruined over the years as holes in the roof had allowed water to penetrate. There was also numerous birds that had at one point made the loft their home.
The roof has now been patched up to fix the leaks. As condensation was an issue in the flat a kitchen and bathroom extractor fan had been fitted. The ducting runs to 2 newly installed pipes int he roof. The loft roof also has roofing nails protruding through the ceiling every couple of inches.

Theres not much in the way of ventilation in the loft. I presume where in the past heat had been escaping into the badly insulted loft in abundance this is what has caused numerous condensation problems in the loft as well as the flat. There are numerous salt build up areas on the roof of the loft.

 

I have spent a few weeks cleaning up the main area of the loft as well as the awkward skeilings. I have safely disposed of the old ruined fibreglass and am now ready to insulate although I need help ironing out a few reservations first.

Apologies to all as I have a few questions. Hope you don't mind I number them. Im just trying not to forget key questions.

 

1) - As I am going to insulate the loft, and I dont want the heat to continue to escape into the loft, after I draughtproof the loft (i have also remedied external repointing and etc of walls) should I lay down a vapour barrier between the joists in the loft before laying down insulation on top of it?

2) - Also, as I cannot reach down into the sloped areas of the loft sides (skeilings) to fit normal insulation, should I lay down foil backed, rigid insulation boards as I cannot reach down that far to install vapour barrio sheet.

3) - Is it definitly a Vapour barrior I would need and not a Damp Proof Membrain?

4) - Should I cut individual sections of VP for in between joists or just one big continuous sheet accross all the joists and neatly stapled to fit? 

5)- I have noticed that where the roofer insatalled 2 ventillation pipes through the roof for ducting, one of the pipes protrudes into the loft to such a degree where it is almost touching the floor of the loft. Obviously this would make it difficult for me to fit insulation under this ducting pipe. Is it possible for me to trim the pipe a couple of inches to allow insulation underneath or should I just insulate around it?

Thank you for your patience and help.

Kind regards,
Teddy

[ProDave]

The biggest issue you need to address, which is so common in Scottish stone buildings, is the "plasterboard tent" that you are living in. 

 

With the gap between the plasterboard (lath and plaster?) and the stone walls open to the loft space, then that space will be full of cold air and your heat losses will be horendous.  I regularly work in this type of building and if you remove a socket or light switch in winter you are greeted by a howling icy cold blast of air.

 

Having the sloping skeillings is not going to make this easy to fix, and sadly the only real solution is strip the ceiling off the skeillings to get it back to the bare frame, seal up the tops and insulate behind the wall voids, insulate in between the rafters and replace the ceiling.

[A_L]

I would say you need to increase the ventilation in the loft. This would prevent condensation on the timbers. On the ceiling the place to put a VCL on the warm side of the lath. Foil backed plaster board would be the sort of thing, although with enough ventilation you shouldn't need a VCL although it will help with air tightness

On the walls you really need IWI, if the insulation has reasonable vapour resistance, e.g. PIR/PUR/XPS you should not need a VCL but again it could help with air tightness.

Simply laying insulation on the skeilings is not airtight enough, either IWI like the walss or remove lath and plaster and re-do.

Tie the airtightness features of ceiling, skeilings and walls together.

 

[PeterW]

I was typing something similar to @A_L and think your best bet here is a new tent inside a tent ..! Insulated plasterboard or at least insulation then new board will be the only way you will get this place warm and dry. 

 

What heating do you have ..? And is this a long term project or just a short term place ..?

[Gone West]

A chap living in Canada who was on another forum used spray foam behind the lath and plaster and apparently it made a huge difference. It obviously requires the right type of foam and care in application.

[teddy_amok]

Hey guys, sorry for the late reply. I was busy repointing today. The whole thing is stressful. The wife didn't realise the structural work that needed done when we moved in. Wouldn't say im handy with the old diy.

 

With all the stress I forgot to put in my initial post that I have spent the last few months researching damp/condensation and insulation I solid wall home. Especially old solid wall homes. Forgot to mention my plan is to drywall/plasterboard over the internal walls next summer or as soon as I can get round to it so for the meantime Im just addressing the airtightness of the loft and getting some proper insulation down having fixed the leaks etc already.

 

Heating is non existent. Its a one bedroom flat. We mostly work and at nights watch tv in the bedroom although now the footy is back on im through the Livingroom watching footy on the tv there. Bedroom has a small gas cylinder fire (not great I know) and Livingroom a small convector heater. We had wall mounted heaters before but they cost a fortune and barely warmed the place up, due to no insulation.

Winter brigs black mould in places and we have multiple small damp traps bought from £shop everywhere. Cupboards, window sills, behind cabinets etc.

 

I had considered the foam option and got a quote. If I remember it was 7k+ (I would not live long enough to cut even going by my current stress levels). I also thought that this might be covering up some existing problems which could be made much much worse and also in solid wall cavities I think there would be cold bridging.

 

100%, new insulation & plasterboard + more ventilation+ proper heating is what I have planned for next year after loft gets done. Loft had uncovered a lot of time consuming problems otherwise I could have attempted the above this year.

 

Thank you all very much for your input and time. Much appreciated.

[Ian]

9 hours ago, teddy_amok said:

Bedroom has a small gas cylinder fire (not great I know) 

If you are finding that the condensation and mould problems are worse in the bedroom then I think the gas heater will be the main cause of the problem. Gas heaters are notorious for causing problems with condensation as they emit large quantities of moisture vapour as part of the combustion process - v approx 1 litre of water vapour for every litre of gas.

 

Have you considered using a de-humidifier as an experiment to try and control the excess condensation?

 

Edit: forgot to say that as well as being great at reducing problems with condensation & mould de-humidifiers can be surprisingly efficient as heaters (better than 100% efficiency) and certainly more efficient than your electric fan heater.

Edited August 27, 2018 by Ian