Attic conversion query

Bonzo Delaney

Hi all I'm looking at an attic conv
the issue is its a high pitched 1930s two story slate roof with no felt in place just laths and what ever lime mortar hasn't fallen out yet
the client doesn't want to strip the roof refelt & slate
has any one done similar and what internal build up was used. it was suggested to spray foam inbetween the rafter and seal it that way but another suggested a cracked slate would let water on to the rafter get trapped and cause rot not noticeable until to late.
I was thinking expanding metal and render sand and cement in between the rafters 4 1/2×2s vapour barrier counter batten for services then insulated slab on internal surfaces.

Anyone done similar or a better idea that doesn't involve stripping the roof ?
ps engineers involved but can't agree on solution so I'm just looking for real world experiences
Thanks in advance
BonzoDelaney.

con1982

I have often wondered what to do in the same situation.

What condition is the slate roof in? If it needs replacing in the next 10 years, you might be better off to re-roof now.

Not sure I would use sand and cement with timber laths. I've heard of people redo-ing the lime parging. Personally I'm not a fan of lime parging because I've inspected so many roofs with it, most of the time the parging is hanging off the rafter or on the ceiling. But these are old properties.

I've also seen many houses with no parging or underlay. A high pitch helps you but there is a risk of leaks damaging your ceiling. Maybe it is worth the risk. Assuming your roof gets damaged in high winds, you might be prepared to suffer some leaking for a short period before it is patched up.

On the other hand. What is the cost of re-roofing? €20k? It would add protection and value to your home.

If it was my house, I would re-roof. If I absolutely couldn't afford to re-roof. I would leave it, patch-up where necessary and save for a new roof when I could afford one.

Hope this helps.

Bonzo Delaney

con1982 wrote: »

I have often wondered what to do in the same situation.

What condition is the slate roof in? If it needs replacing in the next 10 years, you might be better off to re-roof now.

Not sure I would use sand and cement with timber laths. I've heard of people redo-ing the lime parging. Personally I'm not a fan of lime parging because I've inspected so many roofs with it, most of the time the parging is hanging off the rafter or on the ceiling. But these are old properties.

I've also seen many houses with no parging or underlay. A high pitch helps you but there is a risk of leaks damaging your ceiling. Maybe it is worth the risk. Assuming your roof gets damaged in high winds, you might be prepared to suffer some leaking for a short period before it is patched up.

On the other hand. What is the cost of re-roofing? €20k? It would add protection and value to your home.

If it was my house, I would re-roof. If I absolutely couldn't afford to re-roof. I would leave it, patch-up where necessary and save for a new roof when I could afford one.

Hope this helps.

The roof is in good nick small 6x10 slates only the odd cracked one that has already been replaced no leaks in roof . Its good for another generation at least
the spray foam seems a popular solution just wondering has any one done similar and would do anything different
The sand and cement on exp metal in between the rafters was an idea to keep the parging in place on the sloped surfaces behind the vapour barrier

BryanF

Any thing other than re-slate, would be problematic.

(From out - in) breathable felt fitted around joist and tacked, vapour permeable wood fibre insulation, tape & seal vapour barrier, batten, mineral wool service cavity, board

Bonzo Delaney

BryanF wrote: »

Any thing other than re-slate, would be problematic.

(From out - in) breathable felt fitted around joist and tacked, vapour permeable wood fibre insulation, tape & seal vapour barrier, batten, mineral wool service cavity, board

Thanks Brian
is your solution from out in. in the event of not re slating and wrapping the rafters in breathable felt on the under side

BryanF

Bonzo Delaney wrote: »

Thanks Brian
is your solution from out in. in the event of not re slating and wrapping the rafters in breathable felt on the under side

Yes
justification: breathable from vapour barrier the whole way out, considering the lime mortar
Caveat: I'd seek survey, drafted detail & condensation calc from insulation supplier before committing.

Amazing what power a contractor has, if they felt concerned about building regulation conpliance

Part A, C, D & L

(Key words: moisture, condensation)

Edit: http://www.housing.gov.ie/housing/building-standards/tgd-part-d-materials-and-workmanship/technical-guidance-documents

Bonzo Delaney

BryanF wrote: »

Yes
justification: breathable from vapour barrier the whole way out, considering the lime mortar
Caveat: I'd seek survey, drafted detail & condensation calc from insulation supplier before committing.

Amazing what power a contractor has, if they felt concerned about building regulation conpliance

Part A, C, D & L

(Key words: moisture, condensation)

Edit: http://www.housing.gov.ie/housing/building-standards/tgd-part-d-materials-and-workmanship/technical-guidance-documents

Thanks for that Brian
that gives me loads to go on