posted by Malachi Chadwick

saving in old homes: your questions answered

Home energy experts Mukti Mitchell and Chit Chong advise 10:10ers on how to make their old houses more efficient

Check out our interview with Mukti Mitchell: How old homes can conquer climate change

Mukti Mitchell

Mukti Mitchell

Old houses are amazing, but those draughty chimneys, rattly windows and ancient boilers can play havoc with your carbon cutting plans.

We're always hearing from people in old cottages and Victorian terraces, who want to make their homes more comfortable and efficient without sacrificing the historical character that makes them so appealing in the first place.

This stuff can get pretty technical, so I put your questions to home energy experts Mukti Mitchell and Chit Chong, who specialise in making old buildings more efficient.

Chit Chong

Chit Chong

Mukti is director and co-founder of CosyHome Company, which offers insulation products and services specially designed for period properties. Chit is an environmental advisor and qualified engineer with more than 20 years of experience in the field, including the amazing low energy Victorian house in Camden. He now runs Dorset Draughtproofing and Transition Bridport.

Your questions

We invited 10:10ers on Facebook and Twitter to submit questions for Mukti and Chit. Here's what you wanted to know...

Question tweeted from @spentrails:  How about insulation ideas for a ground floor flat with solid walls? Double glazing + carpets seem to be best option.

As with all low energy retrofits, there are site specific issues for ground floor flats, and important issue is whether the floor is solid or suspended timber and the degree of work being planned - often dictated by whether you'll be living there whilst the work is being done.

Whilst double glazing and carpets are a good start, draught proofing and insulation of suspended floors will be a benefit and for solid floors, the addition of thick underlay and/or insulation. Internal or external solid wall insulation are required to make flats really low energy and will make them really cosy and eliminate many of the condensation and mould issues associated with cold walls, but this should be considered as part of a comprehensive low energy strategy, that includes heating, ventilation, lighting, appliances and renewable systems.


Question tweeted from @Chairman_Meeow: does cavity wall insulation increase damp ?

Cavity wall insulation can lead to damp issues in rare cases. For example, the insulation could offer a path for wind driven rain if the external wall is highly porous, poorly pointed or cracked, or the building is extremely exposed. This risk may be reduced if bead insulation is used instead of fibre, but there isn't much research on this.

In buildings where part of the wall is solid, for example in ring beam construction, the warmer insulated walls may accentuate condensation at the corner of the wall with the floors and ceilings. Finally, the insulation may reveal building faults such as blocked weep holes or missing cavity trays.


Question tweeted from @mbanfield30: When is it best to swap an old boiler for a new one considering embodied energy and the shorter lifespan of new ones?

Modern condensing boilers can achieve efficiencies of over 90% in ideal conditions, while old boilers range from 65% for really old boilers to about 80% for the best non-condensing boilers. So replacing an old boiler for a new condensing model of the same output would save 28%. For a 24kW boiler, that's 10kwh per hour of operation.

Accurate assessment the trade off between embodied energy of products depends of the materials used to make them, how they are processed and how they are delivered. This is a complex analysis, however, a rough estimate can be based on the embodied energy of the materials used. Some of the materials in modern boilers like the aluminium heat exchangers have a high embodied energy of 200 MJ/kg whilst the steel body has an embodied energy of 32 MJ/kg. If we assume that the average is somewhere in between, that's an embodied energy of 120MJ/kg, This means that for a typical system boiler with an output of 24 KW, the embodied energy is about 1,200 kWh.

Even when you take manufacturing energy into account, it's worth replacing an old boiler as soon as possible.

At 5 hours operation per day, this will mean a carbon pay back of about 24 days. So even when you take manufacturing energy into account, it's worth replacing an old boiler as soon as possible. It can be argued that their long life of up to 20 years compared to modern boilers with a 12 year life lock people into a high level of emissions.


Question tweeted from @Lindsay_Travis5: Please ask @muktimitchell what Victorian terrace owners should do with disused chimneys, to remove drafts but prevent damp. Thanks!

Perhaps the most cost effective way of minimising draughts from a disused chimney is to use a chimney ballon. Ideally the the top of the chimney should also be caped with a rain proof ventilated cowl to minimise the risk of damp. That said, the manufacturers of chimney balloons do not call for cowls to be fitted and claim that there is usually sufficient ventilation passing the balloons to prevent damp.


Question from Lesley Darling posted on Facebook: Our Edwardian semi has single skin walls so how do we insulate without altering the outside?

While external wall insulation is easier where there is a rendered finish, internal wall insulation is quite possible for solid walls finished in brick or stone.  Fit 2-4 inches of insulation combined with breathable membranes and cover with plasterboard or fibre board.  Radiators and electricity sockets will need to be moved and window sills extended internally.  

One advantage of internal wall insulation is that you can fit selected rooms only. It seems counter-intuitive, but you should insulate the warmest, most lived-in rooms first, since these are losing most heat.  The saved heat will then spread to other rooms.

A professional specification from an architect or insulation expert is necessary to avoid the risk of moisture being trapped between insulation and wall, a problem specific to internal wall insulation. If you cannot obtain a specification locally, we may be able to help depending on your location.


Question from Sally J. Hall posted on Facebook: I want to keep my sash windows but how do I prevent draughts and make them more efficient? Also, we have not cavity walls and no loft - the top rooms are right in the roof. Any tips further to Lesley's question?

It is for this very purpose that I started CosyHome Company, to offer an elegant, unobtrusive and efficient secondary glazing that fits onto sash windows and allows you to use them normally. We're mainly working in the south west of England at the moment, but we hope to expand nationally over the next few years.

Alternatives are aluminium-framed secondary glazing from companies such as Storm Windows. These do allow you to keep your sash windows, but they are much more noticeable on the inside. 

For vaulted ceilings, Thermal Laminate Boarding (TLB) is a good solution.  TLB is an insulation board like Celotex or Kingspan with a sheet of plasterboard glued onto it.  The installer simply screws the boards to the underside of your vaulted ceiling and then plasters over.
If your solid walls have a rendered finish or you are happy to change to a rendered finish then external wall insulation will work. This involves (a) glueing insulation boards to your outside walls, (b) fixing a render mesh on top of the boards using long screws through the boards into the wall, and (c) rendering over.
Question from Yasmin Emerson posted on Facebook

My understanding so far is that the Green Deal applies to homes of any age. This is necessary because almost half of Britain's homes are over 100 years old. I believe that the maximum amount of the loan is £10,000 which may not go as far on an old house as a new one, since extra work is required to preserve the character of the building.

However insulation is now such a good investment (because you save so much in fuel costs) that it is very financially viable even without a Green Deal loan.


Question from Jeremy Langley posted on Facebook: We have big old beautiful sash windows at the front of the house and traditional casements at the back which need replacing. Is it worth forking out for high spec double or triple glazing in part of the house if you know you've got bigger heat leakages elsewhere?

It is always worth insulating part of the house and leaving other parts uninsulated, for the same reason that it's worth putting on a hat even if you don't have any gloves.  But on a cold winter's day you need hat, gloves and scarf!  So if your casement windows need replacing, get high spec double glazing.  

It is always worth insulating part of the house and leaving other parts uninsulated, for the same reason that it's worth putting on a hat even if you don't have any gloves.

I would also recommend having them made in FSC oak from the EU. It'll cost about 20% more, but should last much longer – I have seen modern softwood windows rot out in five years. The double glazing specification should include 18mm void, warm-edge spacer bar, argon filled and low-E glass to get the best insulation value.


Question from John Cole posted on Facebook: We have a Victorian mid terrace with condensing boiler and secondary glazing behind sashes. Worst issues are gaps in wooden floors downstairs, open chimneys (we do not light fires) and original attic room with no insulation to speak of ( needs internal insulation on sloped ceiling). What is it best order to tackle based on return on investment and what are the best solutions? Many thanks.

The most cost effective solutions in order of priority are draughts, lofts (normal), glazing and then walls.  Your secondary glazing has reduced the heatloss from both the glazing itself and draughts around windows, which is excellent.  

I would first fit chimney balloons to the unused chimneys. Then tackle the floorboards and skirting boards using deck caulking from yachts, which is expensive but is designed to expand and contract a lot and stand the test of time. Skirting boards can be sealed using decorator's caulk. Bear in mind that old properties need some ventilation, but there should still be some from doors and electrical sockets (sounds mad but sockets are a big contributor to draughts!).

After that you have a choice with the attic rooms.  If you never use them, then you can lay 300mm loft insulation on the floors.  If you do use them, then use Thermal Laminate Boarding (TLB) or natural insulation boards such as Pavatherm. The latter is more environmentally-friendly and eventually bio-degradable. The former is more efficient per inch of thickness.

We're planning to do more of these 'ask an expert' features in future – which piece of the carbon-cutting puzzle should we focus on next? Let us know on the 10:10 Facebook page.


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