If your heating bills are eye-watering and certain rooms never feel properly warm, poor insulation is probably the culprit. An uninsulated home can lose a third of its heat through the walls and another quarter through the roof. That's money disappearing whilst you're sat there in a jumper wondering why you're still cold.

But here's the thing: there's no one-size-fits-all solution. What works for a 1930s semi won't work for a Victorian terrace. And getting it wrong can create bigger problems than you started with - think damp, mould, and wasted money.

Here's what you actually need to understand about insulating your home.

First: Work Out What You're Dealing With

Before thinking about solutions, you need to know what type of property you have.

Cavity walls (most homes built after the 1920s): Two layers of brick with a gap between them. If that gap is empty, filling it is usually straightforward and cost-effective.

Solid walls (typically pre-1920s): No gap to fill. Insulating these costs more and involves either building inwards (losing room space) or adding to the outside (changing your home's appearance).

Your roof/loft: Usually the easiest place to start. If you've got old thin insulation or none at all, this is often where you'll see the quickest return.

Your floors: Often forgotten, but cold floors make a room feel freezing even when the air temperature is fine.

The type of walls you have fundamentally changes what's possible and what it'll cost. This isn't something you can fudge.

The Critical Thing Most People Miss: Ventilation

Make your home more airtight without adequate ventilation and you'll trap moisture inside. That moisture has to go somewhere - usually condensing on cold surfaces, creating damp patches and black mould.

If you already have condensation on windows, existing damp issues, or no extractor fans in bathrooms and kitchens, these need sorting alongside insulation. One without the other creates problems.

This is why insulation shouldn't be treated as a standalone job - it's part of how your whole house works as a system.

Where to Start: Loft, Walls, or Floors?

Loft insulation is usually the obvious first step. It's the least disruptive, most cost-effective improvement for most homes. If you've got old thin insulation (or none), topping it up to current standards (270mm) makes an immediate difference.

Cost: £300-£1,000 depending on whether you DIY or hire someone.

Once your loft is sorted, walls are typically next - but which approach depends entirely on what type of walls you have.

If You Have Cavity Walls

Filling empty cavity walls with insulation is relatively straightforward. Installers drill small holes in your external walls, inject insulating material, then seal the holes with cement. The whole job usually takes a few hours.

Cost: £1,500-£3,000 for a typical house.

Important: Not all cavity walls are suitable. If you're in an exposed location or have existing damp, filling the cavity can make problems worse. A proper survey should identify whether your walls are suitable before any work starts.

If your walls are suitable and currently uninsulated, this is usually a no-brainer. Good return for reasonable cost.

If You Have Solid Walls

This is where it gets expensive and you need to make some decisions.

Internal insulation means adding insulating boards to the inside of your external walls, then covering with plasterboard. Each external wall loses about 10-15cm of room space. Each room needs clearing out, radiators need moving, electrics need extending, and you'll need to redecorate afterwards.

Cost: Around £7,500-£10,000 for a semi-detached house.

External insulation means attaching insulation boards to your outside walls and covering them with render or cladding. No loss of room space, no internal disruption, but it changes how your home looks (may need planning permission) and costs significantly more.

Cost: £14,000-£20,000 for a semi-detached house (smaller terraced properties less, larger detached homes significantly more).

There's no obviously right answer here. Internal is cheaper but you lose space and face major disruption. External is expensive but protects the building fabric better and doesn't affect your living space.

What About Floors?

Often overlooked but worth considering, especially if you have cold ground-floor rooms.

If you have suspended timber floors (floorboards with a void underneath), you can insulate between the joists. This means either lifting floorboards or accessing from below if you have a cellar.

Cost: £800-£2,500 depending on access and size.

Solid concrete floors need insulation boards laid on top, which raises the floor level and can create issues with doors and skirting boards.

Cost: £2,000-£4,000 depending on area.

Floor insulation is disruptive but makes rooms feel noticeably warmer - cold floors affect how comfortable a space feels more than most people realise.

What Will It Actually Cost?

Being realistic about the full picture:

Loft insulation top-up: £300-£1,000

Cavity wall insulation: £1,500-£3,000

Internal solid wall insulation: £7,500-£10,000 for a semi

External solid wall insulation: £14,000-£20,000 for a semi

Floor insulation: £800-£4,000 depending on type

Full house package: Budget £10,000-£30,000+ depending on your property type and what's already there

These assume professional installation. DIY loft insulation can save money if you're comfortable tackling it yourself.

What You'll Actually Save

Your savings depend on where you're starting from, but realistic examples:

Loft insulation: Around £200-£300/year

Cavity wall insulation: Around £300-£450/year

Solid wall insulation: Around £400-£600/year

Your actual savings will vary based on your home's size, how much you heat it, and current energy prices.

Beyond the bill savings, you get a home that's actually comfortable. No cold spots, fewer draughts, more even temperatures. Most people say the comfort improvement matters more than the money saved.

Getting the Order Right

If you're planning multiple improvements:

1. Loft first - easiest, most cost-effective, least disruptive

2. Sort any damp or ventilation issues before touching the walls

3. Then walls - cavity first if suitable, then consider solid walls

4. Floors last - most disruptive but worth it

5. Heating system after insulation - especially critical if planning a heat pump, which needs sizing based on your home's heat loss. Do the insulation first and you'll need a smaller, cheaper heat pump. That said, if insulation upgrades are prohibitively expensive, you can still install a heat pump - it'll just need to be larger to compensate for the heat loss.

The key principle: reduce heat loss before upgrading how you generate heat - but if budget constraints mean choosing between the two, it's not all or nothing.

Common Mistakes to Avoid

Insulating without fixing existing damp issues first. You'll make them worse, not better.

Forgetting about ventilation. Your home needs to breathe - trap moisture inside and you'll create mould problems.

Choosing the cheapest installer without checking credentials. Poor installation can cause serious issues. Look for TrustMark accreditation.

Doing one room at a time with solid wall insulation. The disruption makes this tempting, but doing the whole house at once is more cost-effective.

Ignoring your loft because it's "only got old insulation." Topping up from 100mm to 270mm makes a massive difference for relatively little cost.

How to Know What Your Home Actually Needs

The right approach depends on:

• What type of walls, roof, and floors you have

• What insulation (if any) is already there and its condition

• Whether you have any damp or ventilation issues

• Your budget and timeline

• Which improvements give you the best return for your situation

Every property is different. A proper assessment should use thermal imaging to see where heat's actually escaping, check for damp, and give you recommendations specific to your home - not generic advice that may or may not apply.

Want to find out what would actually work for your property? We assess your home and create a plan that makes sense for your situation - tackling insulation in the right order, alongside ventilation and any other improvements that fit together. See how Furbnow works.