EWI on Stone walls with slate roof

theRed73

I'm in the process of buying a house that is substantially a stone cottage (rendered, not aesthetic stone) with a newer CW extension. I'm thinking wrt the extension to pump the CW and apply EWI.
I'm also looking at applying EWI on the main cottage and would like to maximise the thickness plus remove the roof soffit to allow the EWI continue up to meet the insulation in the attic and remove the cold bridge in at the eaves.
However, it has a slate roof and i don't know if it is possible to extend the rafters so i can add on another row of slate to accommodate the EWI.
The other consideration is that the upper floor in effectively in the attic (vaulted) so it is a warm roof. There are a lot of broken/missing slates so i plan to:
- strip the slate
- remove the existing rock wool/fiberglass
- add 2x1s to the outer inside edges of the rafters to enable a ventilation space between the membrane and the insulation
- apply a new breathable membrane
- re-install slate tiles
- increase the depth of the rafters on the interior
- install a rigid insulator butted up against the 2x1s and taped
- install plasterboard with VCL

My questions:
Can i increase the overhang of a slate roof by extending the rafters?
How would i extend the slate roof at the gable end (currently flush with a ridge on the gable end wall)
If i'm maintaining the pitch then no requirement to apply for planning (cork)?
If i were to re-install the recent uPVC windows flush how would i fix them to the EWI?
What rigid insulator material/thickness should i shoot for between the rafters?
How do i maintain air tightness/VLC/thermal value where light fittings will be installed?
What EWI material/thickness should i shoot for?
What EWI extruded material/brand is best for extending EWI to below the dpc line?

I'm on a tight budget so looking to do as much as possible myself hence the questions. I know i'm asking a lot in this post but would appreciate your input, advice and corrections.

Thanks in advance!

Calahonda52

The critical issue here is what the wall construction is here and whats the position in the cottage wrt DPC/DPM in walls and floors
In a word, it may not be suitable for a non breathable EWI construct.
Is there any insulation internally?

https://www.nsai.ie/S-R-54-2014-Code-of-Practice.aspx will help with refurb

Trevor Hickey has a leaving cert book which will also help, plenty copies come available for about a tenner as the LC students fund their Megaloop summer gig



The windows are fixed to the wall, not the ewi


You need to grasp the basics of the science here a bit as well:
No point in talking about vcl and breathable membranes and rigid insulations unless you understand the science, which in a word that if the moist air gets past the vcl, which it will, then the rest of the material in the buildup needs to allow this moist air pass through, so if you tape up as described using foil back rigid eps or XPS or whatever, then that layer is pretty much 100% vapour/air proof so the vcl is a waste of money

also lots of stuff on SEAI website

see attachment

Lots of info here too: eircode C15 Y678 in g-maps

Finally
http://www.josephlittlearchitects.com/articles

has a raft of articles, especially for older walls.

While you may wish to to the work yourself, you may need to take some focussed professional advice on materials and techniques..
ps lights etc are best dealt with inside a service cavity

Keep well and good luck

BryanF

theRed73 wrote: »

My questions:
1. Can i increase the overhang of a slate roof by extending the rafters?
2. How would i extend the slate roof at the gable end (currently flush with a ridge on the gable end wall)
3. If i'm maintaining the pitch then no requirement to apply for planning (cork)?
4. If i were to re-install the recent uPVC windows flush how would i fix them to the EWI?
5. What rigid insulator material/thickness should i shoot for between the rafters?
6. How do i maintain air tightness/VLC/thermal value where light fittings will be installed?
7. What EWI material/thickness should i shoot for?
8. What EWI extruded material/brand is best for extending EWI to below the dpc line?!

1. Yes. Details will be important though
2. Get an arch to do the detail and give it to carpenter/roofer
3. Probably not but assessment required by local arch in order tounderstand context.
4. Timber battens wrapped in membrane
5. Assuming your stripping the slates and adding counter batten with breathable felt. Mmineral wool would be a good option
6. Tape, sealant, grommets and membranes - an air-tightness installer could help/ advise here
7. Mineral wool or cork with breathable render - thickness min 100mm up to 200mm depending on size/footprint and your requirements
8. EPS is suitable. Whatever brand you go with for the main walls will have a dpc level product also.

theRed73

Thanks both for your comprehensive responses.

One nugget I omitted was that the external render is concrete based over a (previously) breathable stone wall. Significant interior wall area appears to have a lime based plaster and some rooms are batoned with deal/pine cladding. Some insulation could exist behind those boards. I'll know later this week.
From what I've gather here/elsewhere if breathable insulation is to be used then the entire construction of the wall must be breathable. Given that a concrete render is in place then it is no longer a breathable structure.
As I see it my options are:
• remove/replace the concrete render with a breathable alternative and use a suitable EWI solution, or
• leave the existing render in place and use EPS

Re; DPC/DPM, being a stone cottage I assume not in place/effective except in the new extension. I will install UFH so expect to lay down a new insulated floor.
This does beg the question how do I address the lack of a DPC in the walls?
I've read that putting a French drain below the floor level and around the exterior would mitigate rising damp but how true is that? What options do I have?

@calahonda52: I hadn't considered the rafter boards being foil backed and my notion of taping was more to do with air tightness than VLC. But it would simplify the service cavity then as I could rely on the foil on the insulation and use regular plaster boards.
Although in principle aren't you supposed to stop vapour at the earliest point?

BryanF

theRed73 wrote: »

Thanks both for your comprehensive responses.

One nugget I omitted was that the external render is concrete based over a (previously) breathable stone wall. Significant interior wall area appears to have a lime based plaster and some rooms are batoned with deal/pine cladding. Some insulation could exist behind those boards. I'll know later this week.
From what I've gather here/elsewhere if breathable insulation is to be used then the entire construction of the wall must be breathable. Given that a concrete render is in place then it is no longer a breathable structure.
As I see it my options are:
? remove/replace the concrete render with a breathable alternative and use a suitable EWI solution, or
? leave the existing render in place and use EPS

Re; DPC/DPM, being a stone cottage I assume not in place/effective except in the new extension. I will install UFH so expect to lay down a new insulated floor.
This does beg the question how do I address the lack of a DPC in the walls?
I've read that putting a French drain below the floor level and around the exterior would mitigate rising damp but how true is that? What options do I have?

@calahonda52: I hadn't considered the rafter boards being foil backed and my notion of taping was more to do with air tightness than VLC. But it would simplify the service cavity then as I could rely on the foil on the insulation and use regular plaster boards.
Although in principle aren't you supposed to stop vapour at the earliest point?

Have you engaged an arch with conservation experience?

theRed73

Not yet, I've an engineer assessing the property tomorrow. Architect is next on my list once i have the engineer's report.