Retrofit + Extension: approach

Raoul Duke III

Just looking for thoughts from people who may have done, or be in the process of doing, something similar.

We (family of 5) bought a secondhand house in 2019 - moved in May of that year.

• Early 1970s semi-D, Dublin. Great location for our work, schools etc.
• 4 bedrooms, approx 1600 sq\ft
• Small kitchen extension at rear
• Big back garden
• OFCH
• BER = E1

The house is, while structurally sound, dated to say the least (we were 100% aware of this upon purchasing!). After spending the covid winter here, it's also very apparent that this dating applies to the fabric of the house as well as things like kitchens, bathrooms etc - it is poorly insulated, the windows are ancient, the heating system is creaking.

In short, it requires an entire modernisation effort.

We engaged an architect in early 2020, just before covid hit and we agreed design and plans with him.
In short:

1. demolish existing rear extension, replace with a new 38 sq/m extension (kitchen + living space)
2. replace existing main bathroom upstairs
3. build new ensuite for main bedroom upstairs
4. we do not plan to convert attic at this time
5. some movement of walls downstairs (build new downstairs WC, utility room), upstairs essentially retains same floorplan

This design gave us everything we want from a design perspective. We planned to then move to tender, with more detailed drawings and specifications.

Then covid hit and everything shut down. We just sat tight in our cold house and awaited normality to return. Saving hard against 'the house fund'.

We've now re-engaged with the architect and had a meeting a couple of weeks back. We agreed that the design would remain as is but we also focussed on the fabric of the house as well - the brief being that we want to achieve as high as energy rating as is possible. He thought low A\high B would be achievable, including:

• replace suspended wooden floor with poured concrete
• heat pump
• underfloor heating downstairs
• seal the thermal envelope for airtightness
• new ventilation system
• insulate to A standards (could be external front and back, but would need to be internal on gable wall due to narrowness of side passage)
• new windows\doors throughout

This^^ as well as the obvious bits - being new flooring throughout, full rewire, the extension itself, cost of a new kitchen, cost of new bathrooms etc. I can give more detail as needed.

He is in the process of producing tender plans and documents.

My questions being:

1. timing: everything I read suggests this is a uniquely bad time to be tendering for works like this, both from a builder availability and costs perspective. Is it even worth proceeding now or (given that the house is livable today) would it be smarter to wait 2-3 years until some kind of normality returns?
2. Retrofit grants: it seems to me that we are quite constrained by current SEAI regulations - you have to go through a specific list (small) of approved contractors - and also that the actual grants themselves are not all that generous. Again, is this something worth waiting for?
3. Piecemeal implementation. Is it worth taking a piecemeal approach to the project? My gut says no and that a 'do everything, do it once' approach will ultimately be the least disruptive
4. Costs: I am fully braced for this to come in at well over 200k. I think the question for me really is 'at what point does this project become ridiculous versus the actual market value of the house?' MV is approx 750k.

Thanks in advance!

Calahonda52

The target should be A1 for this scale of refurb
the extension is key to getting it right
mixing ewi and iwi creates thermal bridges
IIRC you wont get an ewi grant unless its all the way around
whats the roof detail for the extension?
will the ewi be used in the extension?
concrete floors seems overkill unless the floors are rotten, they will take months to dry out
the 200 on 750 is a moot argument if you are taking a 30 year view which this project needs.

do the math on a 30 year energy savings vs the different BER
A1 < 25
A2 > 25
A3 > 50
B1 > 75
B2 > 100 kWh/m2/pa

So B2 is 4 times A1 so for 200m2 is euro 3,000 pa vs 750 pa assuming 15 cents kWh
so do a NPV calc on this over 30 years, with carbon tax going to euro 280/ton by 2050

Its a n esy calc which will show that the 200 vs 750 is moot


With 5 in family think about solar thermal with a thermal store: you need a good plumber

Airtightness is key, followed by insulation and think of attic insulation as a wooly hat, and the ewi as a wooly jumper, the two need to meet at the eaves.
I would go for roof tile roof vents and not soffit vents, it negates the need for ventilation baffles.
Good luck

Raoul Duke III

Thanks Calahonda

Calahonda52 wrote: »

The target should be A1 for this scale of refurb

That would be nice.
However I don't know what the tradeoff is between, say, A3 and A1 - especially in terms of cost.
A3 looks pretty good from where I'm sitting right now.

Calahonda52 wrote: »

the extension is key to getting it right
mixing ewi and iwi creates thermal bridges
IIRC you wont get an ewi grant unless its all the way around

thanks - this is great feedback. I will take this point to the architect and ask. I cannot find it in the tender plans.

Calahonda52 wrote: »

whats the roof detail for the extension?

this will mean more to you than me:

FLAT ROOF CONSTRUCTION TO COMPRISE OF TROCAL TYPE 'S' PLASTICISED PVC 1.5 MM THICK, MECHANICALLY FIXED, WATER PROOFING LAYER, ON 100mm KINGSPAN THERMAroof TR26 zero ODP AS MANUFACTURED BY KINGSPAN INSULATIONS, ON VAPOUR CONTROL LAYER, ON A 20mm MARINE PLYWOOD DECK FIXED TO TOP MEMBER OF ROOF TRUSSES.

Calahonda52 wrote: »

will the ewi be used in the extension?

don't know, to same point as earlier. One for architect.

Calahonda52 wrote: »

concrete floors seems overkill unless the floors are rotten, they will take months to dry out

no indication that they are rotten, guess we won't know until floors are taken up

Calahonda52 wrote: »

the 200 on 750 is a moot argument if you are taking a 30 year view which this project needs.

do the math on a 30 year energy savings vs the different BER
A1 < 25
A2 > 25
A3 > 50
B1 > 75
B2 > 100 kWh/m2/pa

So B2 is 4 times A1 so for 200m2 is euro 3,000 pa vs 750 pa assuming 15 cents kWh
so do a NPV calc on this over 30 years, with carbon tax going to euro 280/ton by 2050

Its a n esy calc which will show that the 200 vs 750 is moot

if it was 200 on 750, I would bite your hand off

I think my fear is that it's more like 300 on 750, in which case I am wondering why not keep the 300, sell the house and go find a better house!
It is not a €1m road.

Calahonda52 wrote: »

With 5 in family think about solar thermal with a thermal store: you need a good plumber

we asked about solar, the house is angled East-West which is apparently not ideal?

Calahonda52 wrote: »

Airtightness is key, followed by insulation and think of attic insulation as a wooly hat, and the ewi as a wooly jumper, the two need to meet at the eaves.
I would go for roof tile roof vents and not soffit vents, it negates the need for ventilation baffles. Good luck

thank you

The point about EWI vs IWI is the first thing I need to get our architect to confirm.

At present the side passageway fits a bin by millimetres so that would be useless with EWI.