Attic advice

[DaveG]

Hi all, so the 1870s property I have came with a loft conversion. “Properly” done as in the floor was reinforced with steels and I have paperwork from the sale. But it was done in 1990 so ideas on insulation and ventilation I would guess were questionable at best at the time it was done.
The plasterboard does show some water staining on the ceiling in certain places and if I had to guess I’d say this may be condensation behind the plasterboard where warm boards and cold air has condensed but I don’t know for sure.
I’m going to have to start pulling some of it down in the en-suite because I need to install an extractor that can push moist air out through a roof vent tile I’ll need to install. I’m then looking to add some flat ceiling near the top for the extractor and to house some spotlights. I believe they call this an A shape ceiling.
Any advice on what materials should be used would be handy to know. I know modern conversions you’re looking at PIR board but not sure if in an older building I should be looking at more breathable materials. I’m assuming I’ll still need to plasterboard the ceiling as I’m not aware of any other means of boarding an attic ceiling.

 

[DaveG]

Example water stain mark on the not so black painted adjacent bedroom ceiling:

 

[DaveG]

More water staining near velux recess:

 

[Lacan07]

When insulating roofs (as opposed to loft spaces) you typically go for a 'warm roof insulation'. In this type of insulation there's a clearly defined warm side and a cold side. The aim of the game is to prevent the warm, moist, internal air from escaping through the insulation to the 'cold side' where it can condense and cause damage. For this purpose foil backed PIR is employed and all gaps, flaws and bridges are sealed with air tightness tape, or sometimes people use an air tight membrane. Builders are not known to be very thorough when it comes to the last bit of that explanation.

In this scenario I'm not sure breathable materials are necessary or even advisable, there's no such thing as a 'warm roof insulation' with breathable materials. You have to except you're allowing the warm air to pass through the fabric of the building / roof. A breathable material like wood fibre isn't as effective an insulator as PIR, use too little an amount and you have to ask yourself if its worth it, use too thick an amount and you run the risk of moving the dew point into a dangerous area.

I would use wood fibre board for internal wall insulation because your going (usually) on to a double brick wall and lime plaster and 60-100mm is considered a significant upgrade in comfort. Roof tiles and a bit of bitumen felt isn't nearly as well insulated as a double brick wall.

Just my 2 cents, others may disagree.

 

[Ashville87]

Hi all, so the 1870s property I have came with a loft conversion. “Properly” done as in the floor was reinforced with steels and I have paperwork from the sale. But it was done in 1990 so ideas on insulation and ventilation I would guess were questionable at best at the time it was done.
The plasterboard does show some water staining on the ceiling in certain places and if I had to guess I’d say this may be condensation behind the plasterboard where warm boards and cold air has condensed but I don’t know for sure.
I’m going to have to start pulling some of it down in the en-suite because I need to install an extractor that can push moist air out through a roof vent tile I’ll need to install. I’m then looking to add some flat ceiling near the top for the extractor and to house some spotlights. I believe they call this an A shape ceiling.
Any advice on what materials should be used would be handy to know. I know modern conversions you’re looking at PIR board but not sure if in an older building I should be looking at more breathable materials. I’m assuming I’ll still need to plasterboard the ceiling as I’m not aware of any other means of boarding an attic ceiling.

View attachment 14199

We have a very similar set up in the house we moved in to. I’d guess in ours there’s only thin rock wool and no radiators have been installed so looking to upgrade insulation and sort rads out in the future. Out of interest are you planning to notify building control for the work? Or because you’ve got the paperwork just upgrade insulation best you can?

 

[DaveG]

We have a very similar set up in the house we moved in to. I’d guess in ours there’s only thin rock wool and no radiators have been installed so looking to upgrade insulation and sort rads out in the future. Out of interest are you planning to notify building control for the work? Or because you’ve got the paperwork just upgrade insulation best you can?

As far as I know there’s no need to notify building control as the loft is already a useable living space, signed off as so.
The only thing I’m keen to do is get some more ventilation up there and as part of that it’s going to mean some exploratory work and pulling some stuff apart but if some exploration finds it’s functioning well and not trapping vapour against the roof timbers I will mostly leave as is.
I believe it is possibly a lower quality PIR type of board based on what’s been used to section off the eaves.

 

[Lacan07]

As far as I know there’s no need to notify building control as the loft is already a useable living space, signed off as so.
The only thing I’m keen to do is get some more ventilation up there and as part of that it’s going to mean some exploratory work and pulling some stuff apart but if some exploration finds it’s functioning well and not trapping vapour against the roof timbers I will mostly leave as is.
I believe it is possibly a lower quality PIR type of board based on what’s been used to section off the eaves.

yeah, no need to get BC involved.

 

[mh12]

When insulating roofs (as opposed to loft spaces) you typically go for a 'warm roof insulation'. In this type of insulation there's a clearly defined warm side and a cold side. The aim of the game is to prevent the warm, moist, internal air from escaping through the insulation to the 'cold side' where it can condense and cause damage. For this purpose foil backed PIR is employed and all gaps, flaws and bridges are sealed with air tightness tape, or sometimes people use an air tight membrane. Builders are not known to be very thorough when it comes to the last bit of that explanation.

Would you consider fitting the foil backed PIR board to the rafters on a sloped part of the roof which meets the eaves wall? I've read about the importance of leaving at least 50mm gap between the sarking felt and the the insulation material for through put of ventilation.

 

[Stevers]

Would you consider fitting the foil backed PIR board to the rafters on a sloped part of the roof

That's what our builder did on our dropped ceilings in the back bedrooms and bathroom back in 1997. He added 2"x2" to the existing rafters to ensure a 2" air gap. Given the air flow behind from the then newly vented eaves, he didn't make any attempt to make it air tight, but it would have easy enough to do at the time.

 

[mh12]

That's what our builder did on our dropped ceilings in the back bedrooms and bathroom back in 1997. He added 2"x2" to the existing rafters to ensure a 2" air gap. Given the air flow behind from the then newly vented eaves, he didn't make any attempt to make it air tight, but it would have easy enough to do at the time.

Stevers, have you experienced any damp patches on the part of the ceiling where you had PIR insulation fitted between the rafters or any dry rot as result of condensation due to vapour travelling and settling on the rafters?
In the process of deciding between wodd fibre batts between the rafters or PIR type insulation and basically conflicted at the moment.
I think a number of contributers have gone down the PIR type insulation for ceilings / sloped roofs without consequence.

 

[Stevers]

Stevers, have you experienced any damp patches on the part of the ceiling where you had PIR insulation fitted between the rafters or any dry rot as result of condensation due to vapour travelling and settling on the rafters?

No problems with the dropped ceiling in any of those rooms, one of which is a bathroom, and another of which is my gym/pain cave with smart turbo trainer -
only a handful of you will know just how sweaty and nasty that can be! There is often condensation on the single glazed window, but never on the ceiling or walls.