Heatwaves and Edwardian houses - Did we fail to get our insulation right?

When we posted a short reel saying our newly insulated Edwardian house was keeping in the heat “a little too well” during the heatwave, I thought people would nod along and maybe suggest opening a few windows.

Instead, it became one of our most debated posts.

Architects, retrofit specialists, homeowners and enthusiastic armchair experts all piled into the comments. Some chimed in with their own experiences or offered genuinely thoughtful advice. Some saw it as an opportunity to suggest we shouldn’t have rejected their services or gleefully explain why we’d got it wrong. Others accused me of not understanding physics despite my A* in GCSE double science, which I’m moderately proud of. Some blamed our architect and contractors for choices we’d ultimately made.

It got heated and personal.

I never realised people cared so passionately about insulation. Someone has to, I guess. And I suppose living through a record-breaking heatwave will fuel debate among the masses.

That’s social media.

But reading the comments made me realise there was nuance I could never capture in 20 seconds. Not really about insulation. About how renovation decisions actually get made.

Because gold standard advice is one thing. Acting on it is another.

What happened in the heatwave

Before we get into the wider point, it is probably worth explaining what happened.

Since insulating the external walls of our home, it has become noticeably warmer - even on an average day. Our contractors, who have been living here for much longer than we have, can vouch for this and, bear in mind, the heating has never been on apart from for testing.

During the heatwave, our living room reached 35 degrees at its peak. It was toasty.

I took the number one piece of advice shared by retrofit experts everywhere - I swanned off to my mum’s near the coast for a few days.

I also mildly berated my husband for deciding not to install air conditioning, and we bought some better than average-looking portables in case the heat continued into the following week. Style over substance, always.

Why is our house staying warm and getting warmer?

This is where I need to be very clear: I am not a retrofit expert, architect or building physicist. But, contrary to popular belief, I do understand a little bit about how insulation works. Here's what I think is happening.

Our house has four large south-facing bay windows and by goodness do they get some sun. Being an end of terrace, we also have two large windows on the side. We’ve also acquired seven new skylights and a six-metre sliding glass door, which was always going to change how the house behaved compared with a more traditional Edwardian makeup. All of that sun glare has a lot to answer for.

Before the works, the house had stayed cool during hot spells because it leaked heat through the poorly insulated roof and solid brick walls. Unfortunately, that also meant it was very expensive to heat in winter. Now, the south-facing bays and new glazing are letting in more heat than previously, and the newly insulated walls and new insulated roof are trapping that heat very well.

That was the point of the reel.

Not “insulation doesn’t work”. Not “we have built a disaster”.

Just a slightly wry observation that our newly insulated old house was doing a very good job of keeping heat in - during a week that was hot enough already.

If you did it ‘properly’ you wouldn’t be having this issue

Some of the comments implied that our house should have stayed cool during the heatwave - if we’d made the right decisions.

But “properly” does a lot of heavy lifting in the context of a renovation.

The issue isn’t usually that people don’t care, don’t listen or don’t understand the basics. It’s that renovation decisions happen in layers, and by the time you fully understand one decision, it has often shaped the next five.

You also have to make choices and stick to them, because flip-flopping to alternatives affects cost, programme, contractors and sequencing - we found this out the hard way.

Even when you are given good advice, acting on it usually depends on two things: time and money.

Fabric can’t be decided overnight

Before we started this project, we had no idea how many decisions had to be made upfront - or how much they would shape everything that followed.

But we thought we had enough time to figure it out.

We thought the timings would line up perfectly. Finish renovation planning, start IVF before spade in ground and, with any luck, have a new family member around the time we moved back in.

Then the most wonderful thing happened. We unexpectedly found out we were pregnant - the same month I was due my first fertility appointment.

Instead, this meant the baby would be arriving before spade in ground and before we’d even secured planning permission. I was so far along I’d missed all of my NHS scans.

Like most first-time renovators, we were learning an entirely new language while making hundreds of decisions we’d never made before. But also with only four months to prepare for an important life change.

Pushing back the start date risked losing our preferred contractor - and we all know good ones are like gold dust - to another long-term project. Plus, we didn’t want to push it back because we were excited. We were having the family we’d bought the house for. We didn’t want our son to be five years old before it felt like a family home.

My limited experience tells me that getting the insulation, airflow and heating system right is probably the most complex part of a project, and therefore needs time for proper consideration. 

We sought advice. But did we allow enough time to properly take all of that advice into account? The answer might have been yes - if fate hadn’t had other plans.

Advice is rarely just advice

Something else I don’t think gets talked about enough is that advice nearly always comes attached to a price tag.

People often assume you simply choose the “best” option. In reality, you choose the best option you can justify.

We explored lime plaster, different insulation systems and other ways of balancing thermal performance with budget. Every conversation opened another door, another cost and another consultancy fee.

At some point you stop asking, “What’s perfect?” and start asking, “What matters most to us?”

That’s the question every renovation eventually reaches because bottomless pits don’t exist.

We made choices

People have different priorities. Some people are passionate about achieving the highest-performing building envelope possible, even if it means compromising elsewhere. You know - the kind of people who are always fun at parties.

We weren’t. That isn’t because we don’t care how the house performs. But we also cared a lot about restoring original features, creating a layout we’d love living in every day, preserving the character of a 116-year-old house, and staying within a budget we were comfortable with.

So we chose PIR - more affordable than wood fibre, but something that can come with issues in old properties if not installed correctly. We used plaster, not expensive lime plaster - again, something that can cause issues without ventilation gaps. We didn’t replace the windows with triple glazing, but added vents to all of them to help with ventilation.

Would a different insulation and glazing strategy have performed better in the heatwave? Possibly. Some comments suggested no amount of passive design applied to a retrofit would have made much difference when the day and night heat were so extreme. Others suggested it was avoidable. We’ll never know for certain.

Will any of it matter across a typical year in Wales? That’s the question we’re most interested in answering. Outside of the heatwave, our house has felt much warmer than before, even on cool days. That might not be such a bad thing.

Would spending more money on this part of the build have meant spending less somewhere else? Definitely. Replacing the windows alone, without triple glazing, was going to cost £45k. Goodbye oak panelled hallway, cornice and beautiful fireplaces.

Will we regret not diverting our budget into these things? We’ll find out once we’ve lived through a full year.

So… did we fail?

The honest answer is: We don’t know yet.

We’ve experienced one week of exceptional weather in a house we’ve only just moved back into and we can count on one hand the number of nights we’ve spent at the house since we ‘moved in’. That’s hardly enough evidence to judge how those decisions will play out throughout the rest of the year.

What we haven’t experienced yet is a Welsh winter since we completed these elements of the work.

Our hope is that the same insulation which seems to be holding onto heat during and following the recent heatwave, and seemingly during milder days, too, will also keep the house warmer for longer when it’s cold outside.

We’re gaining heat through the windows quickly and maybe we should expect to lose it just as quickly too - but that’s not what we’re seeing in practice at the moment.

Perhaps by the end of the summer we’ll wish we’d made different choices. Perhaps after our first winter we’ll feel those same decisions were money well spent. Or perhaps the truth will lie somewhere in between.

Either way, we’ll share it. Because that’s what this renovation has always been about. Not pretending we know all the answers. Learning as we go.

Ask us again after we’ve lived through all four seasons.