If you built a new house, you’d expect it to last more than 10-20 years. The same applies to a retrofit, most of the materials last 60 years or more (with routine maintenance), that’s about twice the life of typical solar panels for example. So it makes sense not to evaluate the savings over just 10-20 years, 30 would be a sensible minimum. Retrofits are an upgrade for your house, allowing it to last a lot longer and give you a much more comfortable life.
The current owner may only occupy the building for a short period of time but there are other ways of approaching that. Step-by-step retrofit allows someone else to continue retrofitting after the current owner.
Designing out the need for heating energy is far more advanced even than generating it in a sustainable way.
Retrofits give certainty to the running costs of the building over a very long timescale – this makes them very attractive.
Here are some of the questions REALcosting can answer. The example used is a semi-detached house in Manchester, results for your house will vary. Long timescales are justified because our building stock lasts in excess of 120 years, Victorian houses are not going to be demolished any time soon.
Will the retrofit pay for itself?
This is a main feature of REALcosting, it gives indicative capital costs, ongoing maintenance costs and heating costs for the retrofit over an evaluation period of your choice, e.g. 30 years.
Costs and savings in the future are generally regarded to be worth slightly less than they are today so REALcosting gives all costs in terms of today’s money, i.e. Net Present Value. Doing nothing isn’t free, the semi-detached below is heated to 20⁰C continuously and energy bills and maintenance costs over the next 30 years amount to £45,000 in today’s money. Two of the retrofits are much better value, the deepest retrofit uses a top end MVHR and triple glazing which pays for itself in 30 years.
What if I want my house warmer in winter?
Typically most houses in the UK are heated to an average of 17⁰C over the heating season, including nights and daytime on weekdays when the heating is off. If you’d like it warmer then this extra warmth would be a ‘co-benefit’ and could be included in the calculation if it is worth something to you. REALcosting can allow a monthly figure for this, or it can give the total extra. Co-benefits usually make quite a difference to the economics. The example below assumes the original house is at 17⁰C during the heating season, the retrofits are at 20⁰C and this extra warmth/added style is worth £50/month to the owner. The retrofit has improved the appearance and style as external wall finishes and windows are new in the deep retrofit option. If you’re not sure that the appearance is a co-benefit, consider that the owner could have spent a fair amount of money to get the same appearance without affecting the energy performance of the house at all. Co-benefits make a much stronger case for deeper, lower energy retrofits.
I’m only interested in 15 years
1) Over this sort of timescale most of the measures will have a lifetime much longer than the time you are interested in, some considerably so. What do you want to do at the end of your 15 years if your insulation lasts another 45 years? You could write off the value or you could make an allowance for the fact it will last longer by finding it’s ‘residual value’ after the 15 years. This is effectively a slight increase in what the house should be worth after that time. Having half the life of the insulation left doesn’t mean it has half the value since value falls quite sharply in the first few years, as with the second hand price of anything, then levels off. REALcosting can include the residual value of the components after your evaluation period. The Passivhaus Institute use this method in their Equivalent Price of Saved Energy.
2) It’s probably not going to be economic to use an MVHR or replace the windows with triple glazing, you could try room based ventilation and secondary glazing. Or if the reason is that you might move, see the next feature below.
What if I move in 20 years time?
You’ll probably want to know if it is still worth retrofitting, will you lose money? There’s a special option to include the increase in value of the house. As a starting point it suggests the possible increase in value based on a survey of 300,000 properties across the country. Recent evidence from Hastoe suggests in Bristol it is even higher. In the example graph below the house and retrofits are all heated to 20⁰C and the house is sold in 20 years. You could also allow a figure for the better comfort co-benefit over the next 20 years. Alternatively you might consider retrofitting in stages so that others could continue to improve the house to a low energy standard, e.g. EnerPHit standard.
Does it make much difference what house type I’ve got?
It can do. The example below is for a bungalow, compare it with the equivalent graph for a semi-detached house at the top of this page. This bungalow, like many, has a solid concrete floor throughout and has it’s own window arrangement, otherwise its similar to the semi. In this case all retrofits are all more economic. It won’t always be the case, there are so many variables it’s best to get a calculation done.