or why and how to insulate your floor

Centre for nature and green living

“Housewarming Party” time, or why and how to insulate your floor

Housewarming party participants
Housewarming party participants with Andy Walker (in the middle of the back row)

Written by St Nicks Outreach Officer and founding member of York Community Energy Ivana Jakubkova who organised a DIY floor insulation workshop, aka a “Housewarming Party”, in April 2019. If you want to know more about the process, please get in touch with Ivana or for purely technical queries contact Andy Walker from SURE Insulation who has edited the post for accuracy.

When was the last time you thought about your floor? Do you know what it’s made of? Chances are it’s a suspended timber floor which lacks insulation, with gaps around skirting boards and maybe even between the boards themselves. Often there is just a carpet, underlay and floorboards between your cold feet and the wintry wind whistling through an under-floor void. Air bricks in the external walls (hopefully they haven’t been blocked off) provide ventilation to prevent wooden joists from rotting but they also drive cold air into the house and make us crank up the heating – if we can afford it.

Especially in terraced houses, the ground floor may well be a bigger surface area than your external walls so it’s a good place to start super-insulating your home. Before you do anything, though, I’d recommend getting a whole house energy assessment. It’s important to plot out your plan first, so that you don’t do work that you need to undo later in the process of turning your home from a cold, or costly, house into a comfy home with a vastly reduced carbon footprint.

Heat loss illustration by Caroline Miekina

How does your home lose heat? A lot of carbon emissions from housing are down to heating so insulating a house as well as possible and eliminating draughts can reduce them dramatically. (illustration by Caroline Miekina)

Each house is unique. In a street of seemingly identical buildings, each will have a different pattern of usage, slightly different amounts of heat loss from its constituent parts and thus a different carbon footprint. A whole house energy assessment will help identify the best solutions for your particular house, from easy and cheap wins to more costly but more effective long-term solutions.

Like all human endeavours, eco-retrofitting isn’t without its risks. Insulating a house without providing controlled ventilation, or doing it badly, can for instance lead to problems with condensation and mould. Our aim is to reduce uncontrolled air intake, i.e. draughts, and keep our precious heat in so that we can choose when and how to ventilate. While keeping the whole house plan in mind you can then tackle each room separately, starting with the most used one, and hopefully avoid making mistakes.

Andy Walker conducting a whole house assessment

Andy Walker conducting a whole house assessment – from windows to the attic, all parts of a house get inspected

My house assessment was done by Andy Walker from SURE Insulation who was the technical editor of the Haynes Manual on Home Insulation and has developed a lot of his own, sometimes innovative techniques (you can watch a video about one of his installations here). He advocates super-insulation because current building regulations don’t go far enough to adequately address the climate emergency and truly improve our housing stock. Around a third of all energy use in the UK takes place in households and most of that goes on heating. Insulating them all would go a long way towards cutting carbon emissions and eradicating fuel poverty.


Housewarming Party promo shot

Getting ready to party, with tea! This is the floor to be insulated, with radiator still in its old place under the window (plus Ivana, Tom and Andy of YCE in a promotion shot for the workshop)


Let’s have a “Housewarming Party”!

Andy is also a big fan of engaging communities in insulating homes together because they can do a better job than most contractors who don’t have a good understanding of, or care about, how insulation works. When I first heard Andy talking about “Housewarming Parties” I knew I wanted to host one. My partner needed a bit of convincing that inviting a group of strangers to rip our dining room apart was a good idea but eventually agreed. We don’t fly, drive or eat meat so eco-retrofitting the house is the best way we can further reduce our carbon footprint and improve our standard of living at the same time. The date was set for 6th April 2019 and preparations began.

Andy kindly took care of buying most of the materials needed (see the list at the bottom of the post) while we arranged to borrow extra tools, started clearing the room and arranged for a plumber to move the radiator away from the window. We plan to internally insulate the external wall of the room at some point in the future so it made sense to move it out of the way. Otherwise we’d have to cut up the floor all over again to have it moved later – a clear example of why it pays to have a whole-house plan before you start.

Radiators have traditionally been placed under windows. This was done in the hope that the rising warm air would counteract any descending draughts. However, radiators are better placed on internal walls so that their heat is kept within the home rather than being lost through a cold outside wall. It also means that long curtains can be fitted to further block out the cold. Incidentally ‘radiators’ should really be called ‘convectors’ because the main way that they heat a room is by the warm air rising from them and not by radiated heat.

Thanks to the plumber I now know why English radiators always looked a bit odd to my Czech eyes – both in and outflow pipes are connected at the bottom rather than the inlet being at the top, which is a continental (and non-residential building) norm. This may not look as neat but it allows better circulation of the water inside (and thus more efficient heating) and prevents blockages from rusting bilge build-up. I apologise if I offend any national sensibilities here but to me this illustrates how the quality of English housing keeps falling victim to aesthetics winning over function. I’d rather be warm in a non-chic house than sit in a beautiful but freezing one – I don’t think I’m the only one! Combining the two is the ultimate and achievable aim.

Floorboards as found under the carpet

Floorboards as found under the carpet – just where could draughts be coming from…?

Back to the floor. Our floorboards were not worth saving due to being a mix of damaged original boards and badly laid recent ones. There are some methods for lifting floorboards without damaging them, such as drilling holes around nails so that the boards can be lifted. These techniques are labour-intensive and only worth doing if your boards are worth keeping.

Not having to worry about damaging the floor made it relatively easy to move the radiator and add a new electrical socket in the room – insulation retrofitting is an incentive to get works like that done. It also made the prospect of strangers wielding saws and crowbars at our “Housewarming Party” a bit less daunting.

The idea is very simple – instead of learning about insulation in a classroom, our house served as a workshop for the participants to learn the skills with like-minded people. On the day I provided everyone with food and drink in return for their help – and the sunshine added to a friendly atmosphere.


U-Values explained by thegreenage.co.uk

U-Values explained by thegreenage.co.uk

Up with the floorboards and down with the U values!

Andy started the workshop with an explanation of U values. Put simply, the lower the U value, the less heat flows/is wasted through a material. For example, a typical uninsulated suspended timber ground floor has a U value of around 3.3W/m2K while a properly insulated one will have a U value of 0.14 or less. Understanding this concept opens your eyes to just how bad our houses are when it comes to energy efficiency and how much better they could be, especially if one aims for a Passivhaus standard or similar. Insulating our floor has improved its U value by around twenty times, and increased our thermal comfort in the room.

After a health and safety briefing, the party group was split into two. One was given the task of removing floorboards using circular saws, oscillating multitools and crowbars. While cutting and lifting off the boards was relatively quick and easy, removing nails turned out to be a time-consuming affair. Andy wanted everyone to try out the different tools but the nails were mostly rusted in so levering them out was very difficult and cutting them with angle grinders proved to be the more popular choice.

Removing nails

Removing nails: on the left, doing it the hard way with crowbars. On the right, sparks fly as angle grinding makes the task much easier, speedier and more spectacular.

As boards were getting lifted, lots of rubble was revealed underneath which needed removing. Builders may see this as a free and innocuous way to remove/hide leftovers but rubble can store moisture which can lead to a build-up of moulds, which could potentially find their way into the house. One pile, near where the radiator water had leaked, had a distinct lung-tickling whiff!

Twisting wall ties

Andy demonstrating how to twist wall ties

In the meantime, the other workshop group got busy twisting the ends of wall ties, normally used to help keep 2-layered walls together, by 90 degrees. This simple process turns them into cheap but sturdy holders of wooden battens for keeping the insulation in place. In order to keep air circulating throughout the 40 centimetre deep void under the floor, we were suspending 30 centimetres of mineral fibre directly under the floorboards using a matrix of battens. The size of wall ties and depth of insulation can be adapted to different depth of voids in order to achieve the maximum super-insulating impact.


Measuring up for the matrix

Measuring up for the matrix

Party ends with Matrix and fire

After lunch accompanied with fruitful discussions, our next task was taking care of electrical cables and heating pipes. The cables could overheat if they were surrounded by insulation so we had to run them through conduits to eliminate the risk of fire. Inversely, heating pipes want to be kept well insulated and out of the cold void. According to Andy’s calculations 6 metres of an uninsulated copper pipe (a common occurrence under floorboards) is akin to having a 600mm x 600mm (500 watt) radiator attached to the outside of your house and merrily wasting its heat.

Housewarming Party: matrix

Batten matrix, conduits and pipe insulation in place waiting for insulation to be threaded between the joists and matrix battens

Then it was time to install the “Matrix”. There are different ways to mark out the desirable spacing for the batons – 30cm in this case – but Andy went for the high-tech laser method. He wanted to have roughly 2 battens in between each two hangers. Soon the house was filled with the sounds of hammering and each joist got its share of wall ties. Threading the battens in between joists and cross pieces was a tricky task, mostly thanks to our stubbornness in not wanting to cut them shorter unless necessary. Where they crossed, we used cable ties to secure them so that insulation couldn’t push them apart and drop in between.

Housewarming Party: relaxing by the fire

Housewarming Party: relaxing by the fire

By the end of the party day, the Matrix was in place but most people had gone home and only a few hardy souls were rewarded for their endurance with another meal and drink by the fire made from discarded floorboards. We are extremely grateful to Nicole, Helen, Andy, Martin, Joe, Jamie, Jonny and Tom for taking part in the first York Community Energy’s “Housewarming Party” and helping us improve one York house! There was certainly enthusiasm for holding more so watch the space.


Day 2 – insulation

We’re even more grateful to Andy Walker and friend Andy for sticking with us on the second day. We had hoped to have laid the insulation the day before so that everyone could see it done but insulation is a fiddly job, which needs to be done carefully to ensure air tightness and eliminate potential for condensation forming, so it was a couple of hours of small tasks still before we got down to it. This included dealing with an awkwardly placed air brick, which we wanted to continue providing air flow into the void without creating draughts in the living space. To create a duct for the air flow we used a couple of bits of wood to stop insulation from blocking it off and a small bit of insulation pipe sealed around with silicon.

Air vent

Air vent: 1 – as found before insulation put in place; 2 – wooden planks attached to the floor joist will stop insulation from blocking off the bottom half of the vent in order to keep air flowing into the uninsulated part of the floor void and a bit of foam insulation blocks the top half which would otherwise cause draughts at the floor level; 3 – silicon ensures air tightness

DIY Insulation Day 2: taping sleeves

Andy helping Andy with taping sleeves to prevent scratchy insulation fibres from getting inside clothes

Finally we could don our dust masks, tape up the sleeves and spend a few hours threading the insulation at a right angle under the joists.

We had to make sure that all pipes were either covered or uncovered as required, and make an unexpected shopping trip to get some more mineral wool. When it came to laying the second layer in between joists, Andy Walker got a timer ready and stood back. I’d never have guessed that it would take the rest of us only just under 10 minutes to do this!

DIY Insulation Day 2: layering insulation

Insulation layering: the first layer took a few hours or so to put down (left), the second layer in between joists took about 10 minutes


The return of the floor

Chipboard down

Fitting the chipboard panels proved tricky (left) but eventually we had a solid floor again (right)!

(Another) real challenge came when we started fitting the chipboard. The boards are heavy and ideally need two people handling each. Only a few boards could be put on the floor without any cutting. The rest had to be trimmed and carefully fitted to make sure that the tongue and grove sections were tight together. The other challenges to laying the floor were the uneven walls and badly fitted skirting boards. Most panels needed careful measuring, cutting to shape (e.g. tongues get cut off the boards adjacent to walls) and plenty of swearing, or even “dancing” (watch the video below) to make them fit.

A word of warning: it is surprising just how easy it is to confuse the insulation layer with a solid surface, especially when knackered after a hard day’s work, and I think that all of us accidentally stepped off the joists into it at least once. Luckily, no battens (or Andys) were damaged in the process but it’s something to watch out for.

To ensure air tightness and staying put, all were glued together with PVA and also screwed to the floor joists. Later on Andy showed me how to fill gaps round the edges. I particularly liked his trick of using a bit of string, a piece of board, glue and self-tapping screws to create crosspiece supports for resting pieces of chipboard to plug the gaps.

Gap plugging

Gap plugging: 1 – there is a gap between the edge of the room and the first joist; 2 – a piece of board on string will help plug the gap; 3 – drilling holes where the support piece needs to be attached; 4 – gluing the support to the floor edges will help keep it in place while screws are driven through the pre-made holes (the string held tauht is enough to allow self-tapping screws to bite); 5 – support in place; 6 – a piece of chipboard plugs the gap and foam seals it

The next step was to seal round the edges of the room with a combination of foam and silicon where gaps were too small. After a long while we also made our decision on the choice of floor covering. It wasn’t easy considering the quality and looks of the material alongside its sustainability and ethical sourcing. For example bamboo sounds perfect but comes from China and we couldn’t find any reassurance over labour rights.

In the end, intent on not opting for a dust gathering carpet, we opted for natural linoleum made from 100% natural raw materials including linseed oil. Unlike in vinyl, there are no phthalate or other air polluting chemicals, and the smell takes one right back to lino cutting art classes. Finding an installer willing, and with the time, to fit the lino, which can crack if not handled properly during installation, proved lengthy and certainly not cheap. Finally, just before Christmas the lino got fitted and looks great.

Floor finished with linoleum

Floor finished with natural linoleum


smiley from Pixabay.com




Was it worth it?

So, we did not succeed in hosting a party that would show all the stages of insulating a suspended timber floor. We took a lot longer than envisaged to finish the job and get the house back in order. We spent more money and time than planned on the flooring… Still, despite it all, I think it was well worth the pain and we learnt valuable lessons in how to do it all with less effort next time, including the party workshop.

Ideally, we would have monitored the room and outside temperatures for a while before all the work was done and afterwards so that we could quantify our energy savings. We certainly have plenty of anecdotal evidence of the room being warmer than before. We used to keep the heating thermostat there but now often have to move it to another room because the rest of the house can get freezing cold before the boiler gets switched on. This was observable even before we also changed the shoddy double glazed window and patio door for triple-glazed units which further improved thermal comfort of this and adjacent room*.

Now we have a lovely looking floor and no draughts in at least one part of the house. I am certainly looking forward to getting the other half of the ground floor insulated too. Anyone else up for a housewarming party?

Cosy Up! posterIf you have the same kind of ground floor, I would certainly recommend getting insulation underneath. This measure will make your house more comfortable for decades to come without any loss of space in the rooms, which can be a concern with internal insulation.

For more information on energy assessments, energy saving tips and to express interest in hosting your own housewarming party, please contact York Community Energy. To make a start on a budget, come to our Cosy Up! Draught-proofing workshop on 2nd February.

* Triple glazing is very costly but it’s made a great difference in the rooms where we’ve installed it. The first morning after installation we thought it’d gone wrong because we could see condensation on the patio door but it turned out to be on the outside pane, showing just how cool it was outside while the inside was much warmer. We hope to replace the rest of the windows in the future.


borrowed tools and protective gear

borrowed tools and protective gear

Materials used (cost under £400):

Tools needed:

20 January 2020 | Categories: One Planet Living | Tags: carbon footprint, DIY, draughts, floor insulation, heat loss, housewarming party, YCE, York Community Energy