Can you combine External & Internal insulation?

Velcrow

Hi All,

Any help appreciated, we are getting colder (and poorer) by the day!

I live in a 1940s semi-detached, single leaf cavity block wall type construction house. The front of the house has a porch and an external red brick fascia on the lower half. The side and rear elevations have a dashed render finish.

The problem - I would like to use external insulation but this may not be possible for the front of the house due to planning restrictions (we would be the first on a row of 20 houses to do it) and cost (replicating the brick work and we also have to deal with the porch)

In short, can I use external insulation on the side & rear and internal to the front of the house which is north facing?

Thanks - John

sinnerboy

In short - yes you can your situation is common enough.

Velcrow

Thanks Sinnerboy,

Any obvious pitfalls we should avoid etc . Appreciate any direction here and I will continue research.

It's a "live" project so if its helpful I will add in some before and after pictures and keep people updated on what we learned.

We have been calling into our neighbours and all the houses have 100% internal insulation which would have been completed in the last decade.

rodzer

Cost will be an issue as external insulation is expensive.
Also getting a contractor to quote for 3 walls could prove difficult while getting another quote for 1 wall. Might be best to stick with internal for all walls. Have your neighbours really got insulation inside their "dry lining" or is it just timbers and plasterboard?

beyondpassive

I would only use drylining as a last resort. The brick can be replicated with brick slips and the junction with the neighbours can be hidden with a downpipe. The porch can be saw cut to allow the insulation wrap the building and then prop it up with new steel posts.

sinnerboy

beyondpassive wrote: »

I would only use drylining as a last resort. The brick can be replicated with brick slips and the junction with the neighbours can be hidden with a downpipe. The porch can be saw cut to allow the insulation wrap the building and then prop it up with new steel posts.

And I would balance the need for energy conservation with the need to conserve our built heritage. 70 year old weathered brick does add significant character to a building and in this case to a street scape. As often too does detailing around porches and other features. Some day somebody will be at the sharp end of an enforcement action for disregarding this and I would cheer that action on personally.

OP with modest dry lining (38mm PIR) you will cut the heat loss through the wall by about 66%. ( U Value 1.8 down to 0.6 - approx ) . To arrive at modest (thermal) performance from truly awful is in itself very worthwhile.

beyondpassive

sinnerboy wrote: »

And I would balance the need for energy conservation with the need to conserve our built heritage.

I would agree fully SB, and am appalled by some of the exterally insulated renovations that pay scant regard to the character of the building or the context of the streetscape. Generally these renovations have no professional or design input.

For Victorian or Edwardian buildings it would be visually and technically problematic externally insulate, but for a 1940's Semi-D, EWI may well be a good option if handled sensitively and with a good professional on board.

Velcrow

@ rodzer
Thanks, your right some are just timbers and plasterboard - we have some of this in a room of our own.

@ sinnerboy
Thanks, yes to be honest the balance is one of getting warmer, overall cost and we very much like the front of the house as is. A (thermal) improvement of anything like 66% would be a great outcome. We are still a relatively young family so the other 34% can be gained by leaving on the jumpers

@ beyondpassive
Thanks, your view represents some of what we are reading. One of our biggest concerns with internal is not the performance but the health risks. I have two small children and in our research we read about the link between internal insulation > mould > asthma and the fact it is "banned" in some countries (although I could not confirm this). Can internal insulation be used/installed in a way that mitigates these risks completely. I'm conscious that the construction is single leaf cavity block which seems like the worst for mould.

Thanks John

ShaunC

Velcrow wrote: »

Thanks, yes to be honest the balance is one of getting warmer, overall cost and we very much like the front of the house as is. A (thermal) improvement of anything like 66% would be a great outcome. We are still a relatively young family so the other 44% can be gained by leaving on the jumpers.

sorry, but someone had to point out that 66% and 44% is just a little bit wrong:o

sinnerboy

Ah , but being a Man U fan you understand the concept of "giving 110%"

sinnerboy

Velcrow wrote: »

Can internal insulation be used/installed in a way that mitigates these risks completely. I'm conscious that the construction is single leaf cavity block which seems like the worst for mould.

Yes by not overdoing it. Walls need some heat energy transmitting through them to help keep them dry. Google "Breaking the Mould" to complete your research to locate a learned suggestion that lowering the U Value to about 0.5 W/m2K - but no lower - is about optimum.Personally I would use no more than 38mm PIR i.e. 50mm board being 12mm Plasterboard and 38mm PIR.

But - pay careful attention now

70 year old aged brick will be very porous and the vast bulk of moisture entering your front wall will be from rainfall - not trapped (aka interstitial ) condensation. Keep your gutters cleans and joints sealed. Carefully inspect the brickwork joints and re-point if necessary. Check that all cills are free form cracks and all flashings are intact. Untill you have attended to all his do not attempt dry lining.

Velcrow

@ sinnerboy

Thanks. Currently reading -

Joseph Little's "Breaking the Mould 1"

John

Velcrow

Hi,

Just coming back on my orignal question, and the decision we took.

After reading Joseph Little's "Breaking the Mould 1 -6" - (a great read, very approachable for the layman) we decided not to use internal insulation for our single-leaf cavity walls. Internal could be used but the two key factors that stopped us were

- the impact it would have on the internal space (coving, chimney breast and the 75mm lost on each wall)
- the risk of condensation / mould and the possible health side-effects

As for combining the two - again possible but not a runner for us due to the additional effort involved in overlapping the two methods to prevent cold bridging.

So in the end we went for external and it will be the early summer before it is installed (to take advantage of the Irish weather and the sun drying out the walls!).

Finally, thanks for all the advice here.

John

Dully

As for the hollow core blocks and EWI:
Saw a job done where EWI was installed to hollow blocks. The blocks were in line with each other, leaving a nice "chimney" in the walls.
The wall was "open" at the top, to the attic.
Warmth gets into your wall, raises in the channels of the hollow blocks, disappears into the attic before even hitting the EWI system.
All I want to say here: make sure the blocks are sealed on the wallplate.
A decent EWI installer will take off the soffit/facia and seamlessly connect EWI with attic insulation.

BryanF

Velcrow wrote: »

Hi All,

Any help appreciated, we are getting colder (and poorer) by the day!

I live in a 1940s semi-detached, single leaf cavity block wall type construction house. The front of the house has a porch and an external red brick fascia on the lower half. The side and rear elevations have a dashed render finish.

The problem - I would like to use external insulation but this may not be possible for the front of the house due to planning restrictions (we would be the first on a row of 20 houses to do it) and cost (replicating the brick work and we also have to deal with the porch)

In short, can I use external insulation on the side & rear and internal to the front of the house which is north facing?

Thanks - John

Yes, you can. The type, thickness of drylining and vapour barrier need to be chosen and installed carefully. To maximise benefits joined up thinking is required:wins, floors, attic, draft reduction but also ventilation. overlap the drylining and ewi and consider taking ewi to foundation and beyond eaves level