Retrofitting: the order that saves money
The biggest mistake when retrofitting is starting with the installation. The gain sits in the building envelope, and that determines whether the rest pays off at all.
In short
- Insulating comes before replacing the heat source: a heat pump in an uninsulated house works inefficiently.
- The usual order is: draught-proofing, then roof, floor and walls, then glazing, then ventilation, then the installation.
- With an apartment, work on the envelope almost always runs through a decision of the owners' association.
- Subsidy schemes change regularly, always check the current terms before placing an order.
Why the order matters
A heat pump delivers heat at a low flow temperature. That only works well if the home holds on to that heat. Install one in a house with an uninsulated roof and single glazing, and the unit runs continuously at high output, the saving disappoints and it is not comfortable indoors. Insulation first is therefore not ideology but arithmetic: every step lowers the heat demand, which lets the next step be smaller and cheaper.
The order
- Draught-proofing. Cheapest, fastest to pay back, and immediately noticeable in comfort. Letterbox, crawl-space hatch, frame joints, skirting.
- Roof insulation. Heat rises; this is often the biggest gain per euro. With an unused attic, an insulated attic floor is the cheapest variant.
- Floor and ground insulation. Relatively simple if there is a crawl space, and it immediately solves part of the cold-feet complaint.
- Wall insulation. Cavity wall insulation if there is a cavity; otherwise internal or external wall insulation, which is considerably more disruptive. With cavity insulation, watch the condition of the facade and penetrating damp, have this assessed beforehand.
- Glazing. Going from single to HR++ delivers a lot; from HR++ to triple much less. Also look at the frame: triple glazing in a draughty frame is a waste of money.
- Ventilation. The better you insulate and draught-proof, the more important controlled ventilation becomes. Do not skip this step, it is the source of damp and mould complaints in newly insulated homes.
- Heat generation. Only now: a heat pump (full or hybrid), low-temperature emitters and possibly solar panels.
What this means when buying
At a viewing, look not only at what is there but at what still has to be done. A home with label E where the roof is already insulated and the cavity is not is a different project from a label E home where nothing has been done. Concrete things to check: is there a cavity and is it filled, is the attic or roof insulation visible, is there insulation in the crawl space, what glazing is fitted, and how old is the boiler.
With an apartment
The envelope of an apartment building is communal. The roof, the facade and usually the window frames too are not yours alone, so insulation requires a decision of the meeting and comes out of the association's budget or the reserve fund. So check the minutes and the MJOP to see whether sustainability is on the agenda, that says more about your future heating costs than the label of your own apartment.
Amounts, subsidies and standards change regularly. Check the current schemes before instructing a contractor.
Frequently asked questions
Can I fit a heat pump in an old house?
Technically almost always, but the question is whether it pays off. Without reasonable insulation and low-temperature emitters the saving disappoints. In such homes a hybrid set-up is often a wiser intermediate step.
Is cavity wall insulation always a good idea?
Usually, but not blindly. With facades suffering penetrating damp, cracks or poor pointing, insulating can make damp problems worse. Have the facade assessed beforehand.
Do I have to arrange ventilation if I insulate?
Yes. The more airtight the home, the more you depend on controlled ventilation. Skipping it is the most common cause of damp and mould complaints after an insulation project.
Who pays for retrofitting in an apartment building?
Work on communal parts is paid for by the association, from the budget or the reserve fund, following a decision of the general meeting. You contribute in proportion to your fractional share.
Unsure about the documents for your dream home?
Analyse your property documents