site wide search

Retrofit in Hull

September 13th, 2015. SuperHomes open day at 84 Inglemire Avenue, Hull.

End wall

Thanks to the lovely couple who live there and opened their home to inspire others on the Superhomes open day in 2015. This is one of the very few such initiatives in the area.

Their house is a 1930s semi with solid brick walls and and a (probably) 1970s rear extension with cavity walls (which they insulated with poured polystyrene bead)

Retrofitting an average 1930s semi must be one of the most difficult projects to undertake, particularly in terms of where the priorities lie. This project incorporates a wide range of retrofit features including

  • considerable amounts of insulation including external and internal
  • attention to air tightness
  • new solid floor insulation (existing floor boards lifted, Warmcell fitted on draped draft proof membrane between joists and boards replaced.
  • large increase in loft insulation (up from 100mm to 300mm of mineral wool)
  • an air source heat pump (more on that below)
  • a sensible approach to conserving worthwhile aspects of the building which were attractive or didn’t need replacing (most of the floor boards, skirtings, architraves, existing double glazed windows etc.
  • a limited amount of ventilation heat recovery
  • both pv and evacuated tube solar colectors
  • care about sourcing materials and building skills, locally where possible
  • using natural paint and varnish finishes
  • low water shower head to save water and water butt to water the garden
  • a wood burning stove for the sheer joy of it.

The wall insulation is possibly the most interesting part of this project because of its complexity and their considered approach to it:

The front and back walls have been insulated internally while the end wall has the insulation applied externally. Compared with building a new house there are many complexities and compromises involved with insulation.

see more on retrofit insulation

External insulation is best (and lots of it) but there are some other factors at work:

  • If they had externally insulated the front wall it would have jutted out (maybe 200mm or 300mm) compared with the neighbour’s house, due to the extra insulation thickness. How would planning (permission) view this and how would it look? Another factor involved with this project was that the owners like the look of traditional brick rather than render which normally goes on external insulation. Well of course that’s a matter of personal taste. Render could become the new signifier of eco insulation just as stuck-on concrete stone tiles once became the signifier of someone who wanted to distinguish their newly purchased council house from those around. The back wall probably doesn’t matter visually quite so much so it’s easier to insulate that externally anyway.
  • When you insulate externally you have to allow for the effect of extra wall thicknesses. For instance, at the most obvious, your roof may no longer extend over the walls and will need extending too.  This can create problems in itself especially if the bedroom windows are very close to the eaves. Window sills will need altering and there might be some really tricky areas such as in the picture below where the extra insulation and render meant that a narrower door had to be used in the side extension.

Internal insulation – there are three main considerations:

  • the more insulation you add, the smaller the rooms get. This can be quite significant,
  • you need to do extra side insulation on the internal walls (about a metre in length) so that they do not become heat loss routes (because they connect directly with the external walls). This can create an awkward step in the internal wall.
  • it will damage internal room decorations or features. So the decider here is whether the rooms need keeping as they are or whether they would be better for replastering etc.

Energy-wise, an interesting balance has been struck. Huge savings have been made on the energy bills, not only on heating but also via solar panels, LED lighting and appliances. Check out their web site which gives figures on savings, particularly on CO2 emissions.

The problem with retrofit is about where exactly do you spend your money and how far do you go with it? Arguably, in the case of this house, it might have been better to “go the whole hog” and achieve the EnerPHit standard if sufficient funds had been available. A complicating factor is the Renewable Heat Initiative, which favours add-ons such as solar collectors and heat pumps rather than the “Fabric First” approach which is mainly about insulation.

The space heating is now provided by an air source heat pump which doesn’t come cheap. At about £11,500 (including its hot water storage tank), this has been used to replace the ageing gas boiler. It should have a COP of about 3 but will probably not make any carbon savings over a gas boiler (since it runs on electricity – which is inefficient to produce). These bits of kit are not cheap to maintain either; annual service costs are around £300 compared with £200 for a gas boiler.


air source heat pump

It is interesting to speculate what the outcome might have been if the money spent on the ASHP had gone into extra heat insulation, extra draft proofing and Passivhaus standard MVHR (at about £3750). Possibly it could have achieved EnerPHit standard for the same expenditure.

The interesting thing about Enerphit is that when you get to that high a standard of insulation, a central heating system becomes unnecessary. The little heat needed is injected straight into the ventilation system. Along with solar gain, body heat and heat from appliances, this is enough to provide a high level of heating. See the Europhit web site.

Back to the insulation! A decision was made to retain the appearance of the front and rear of the house by insulating on the internal surfaces of the walls (40mm of wood fibre board), whereas the end wall was insulated externally and rendered. There were no planning permission objections to this. But what happens when you insulate internally is that any internal walls which are directly connected to external ones provide a ready path for heat to escape.

The way to prevent this is to add insulation to the internal wall  for about a metre back from the connection to the outer one. This is what they did.

insulation returned

This of course creates an uneven internal wall finish. A more radical approach is to cut the internal wall away from the external one and fill the gap with insulation. If you do this you will need advice from a structural engineer as the junction between internal and external walls is often used for structural integrity.

The end wall insulation (100mm fibreboard with render), also posed some challenges. It has a capping piece where it extends out beyond the roof overhang and gutter


and its thickness also caused the door on the lean-to extension to need narrowing at the back of the house.

Hull external insulation narrows door

A narrower door due to the thickness of the wall insulation. Note also the rainwater harvesting connection to the fall pipe.

 Solar energy

With help from the Renewable Heat Incentive, both PV and solar thermal panels have been installed. An interesting aspect of the pv panels is that they are on three sides of the roof and that a redundant chimney was taken down to prevent overshadowing of the panels. Micro inverters are incorporated in the pv circuitry.

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>



What is 8 + 4 ?
Please leave these two fields as-is:
IMPORTANT! To be able to proceed, you need to solve the simple calculation above. (so we know that you are a human) :-)