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Last updated on June 14th, 2023

Retrofit insulation cost guide

If you’re fitting insulation retrospectively, costs can be a little higher as your tradespeople will need to work around your existing electrics, gas, water and more. Read on for the average retrofit insulation cost.

If you find your heating’s on max throughout the winter, you might be considering upgrading your insulation. This way, not only could you make a saving on heating costs, but you’ll also be doing your bit to make your home kinder to the environment.

If you’re fitting insulation retrospectively, costs can be a little higher as your tradespeople will need to work around your existing electrics, gas, water and more. Read on for the average retrofit insulation cost.

Retrofit wall insulation cost

ItemUnitCost - lowCost - high
Retrofit cavity wall insulationPer average semi-detached house£800£1,200
Retrofit solid wall insulationPer average semi-detached house£8,000£10,000
Retrofit external wall insulationPer average semi-detached house£10,000£12,500
Retrofit loft insulation - rollsPer average semi-detached house£600£1,000
Retrofit roof insulation - spray foamPer average semi-detached house£3,000£4,000
Retrofit floor insulation - suspendedPer average semi-detached house£1,500£3,000
Retrofit floor insulation - solid floorPer average semi-detached house£2,000£4,000
Carpenter to remove/fix floorboardsPer hour£30£45
Builder for superficial repairsPer hour£30£45

Our costs are ballpark averages – get a local tradesperson to quote now

Wall insulation can be a great way to help keep the heat in your home during the winter, and out during the summer.

Cavity wall insulation involves filling your wall cavities with insulating material. It’s the cheapest option available, costing around £800 – £1,200 for a small, semi-detached house, but it can only be used on houses that have cavity walls (luckily, most houses built post-1920 do).

If you have solid walls, on the other hand, you’ll need to pay a bit more. You’re looking at around £8,000 – £10,000 for solid wall insulation or £10,000 – £12,500 for external wall insulation.

However, you’ll also need to consider how adding insulation retrospectively could affect your house. For example, you might need to budget for adjustments to your home’s ventilation to avoid causing a damp issue.

Retrofit loft insulation cost

Loft insulation is arguably the easiest kind to fit retrospectively, especially if you insulate at the joists. Assuming you have easy access to your loft, you’re looking at around £600 – £1,000 to place insulating material between the joists.

Alternatively, if you’d like to insulate at the rafters (also known as roof insulation) you could pay anywhere between £3,000 – £4,000. This is likely to be a good option if you have vaulted ceilings, for example in a loft conversion. Spray foam insulation sits at the higher end of this price scale.

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Retrofit floor insulation cost

Insulating your floor is a great option if you’re tired of feeling icy cold floors beneath your feet in the winter. The cost to fit floor insulation retrospectively will depend on what kind of insulation method you choose.

Suspended floor insulation

If you have suspended floors, you might experience cold air rising up between your floorboards. To prevent this, you can have the floorboards removed and the space beneath them filled with insulating materials. This costs around £1,500 – £3,000 per ground floor. 

Before accepting a quote, it’s worth checking whether the price includes the removal and replacement of the floorboards. If not, you’ll need to get a carpenter in to handle this for you. This will probably cost around £30 – £45 per hour.

Suspended timber floor insulation

If you have a suspended timber floor, it will most likely be fairly quick and easy to insulate. In this case, insulation can be placed underneath the floorboards and between the timber joists.

In total, you can expect suspended timber floor insulation to cost around £1,500 – £3,000 per ground floor.

Solid floor insulation

Lots of new homes are built with solid floor bases made from concrete or screed. However, you can still add insulation if you want to make your floor feel warmer underfoot.

Retrofitting solid floor insulation involves carefully removing your floorboards to avoid damaging them. A layer of rigid insulation is then placed directly on top of the concrete or screed, followed by chipboard. Your floorboards can then be laid back over the top.

You can expect to pay around £2,000 – £4,000 for solid floor insulation. However, you may also need to budget for new skirting boards and adjustments to doorways and thresholds as adding floor insulation to a concrete or screed floor will increase the total floor depth.

Retrofit insulation cost summary

  • The cost of retrofitting insulation will vary based on the method you choose
  • Consider budgeting extra for superficial repairs at around £30 – £45 per hour
  • Remember that small fixes such as repairing joins at windows can also help to improve your home’s efficiency
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Working with professional estimators, we collate cost estimates for the common home improvement and repair jobs in the UK.

All the costs are estimates only. For accurate costs for your particular requirements, you are encouraged to reach out to professional tradespeople to receive a quote for your job.

Our estimators are Chartered Members (MRICS) of the Royal Institution of Chartered Surveyors and Members of the Chartered Institute of Building (MCIOB). See full disclaimer.

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