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Do you have cold suspended timber floors downstairs?...Solutions here..

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Do you have suspended wooden downstairs floors? By this I mean downstairs floors that aren't solid concrete, but sit on wooden timbers underneath with cold space underneath like the photo below?

Around 1 in 4 homes have either some or most rooms with floor structures like this.

Rooms with floor structures like this often feel cold underfoot, are difficult to keep warm and go cold quickly after the heating has switched off.

This is because the space underneath is ventilated to the outside the house and the air under the floor boards will be very cold in winter.

The depth of this underneath space varies greatly. Some homes have only 250mm depth, some enough space to crawl, and some that are deep enough to be an actual cellar.

They all have one thing in common though. The only the thing between your feet and that cold space underneath is the floor covering and the floor boards. They don't do a good job of keeping the cold out.

This article describes of a range of practical actions and options to improve comfort and reduce energy costs in these situations. Some are quite easy DIY jobs, others more challenging but can still be done yourself.

There are two reasons rooms and floors like this feel cold:

  1. Draughts from around the edges and between floor boards.

  2. Lack of insulation under the flooring - these floors were...sadly...never insulated when they were constructed.

The actions and quick links to the solutions are:


First...checking to see if you have suspended wooden floors

Your floors will either be suspended wooden floors OR they will be solid concrete. Here are a few ways you can find out which type you have if you are unsure:

  • Lift a corner of your carpet and have a look underneath and see what is there. If there is wooden boarding of any sort underneath then that is a pretty strong clue that you do have suspended wooden floors.

  • Jump up and down on it and see how solid it feels.

  • Look at the exterior of the house. Firstly, has it got vent bricks on the outside walls below the level of the floor indoors? If so, and you see a number of them dotted along every few feet then it is pretty likely that you have suspended wooden floors in at least part of your home.

Important safety points if you have unvented gas appliances in rooms

Many of the solutions described below are likely to reduce the ventilation in the room or rooms above these cold underfloor spaces. If you have any form of unvented combustion heater in the room you want to make modifications to, it is ESSENTIAL to ensure that there is adequate ventilation in the room for the appliance being used. This is to prevent the build-up of poisonous carbon monoxide gas.

If in doubt about whether there will still be adequate ventilation, seek advice from an appropriate professional.


The sources of draughts

Downstairs rooms with suspended floors usually have gaps around the edges of the skirting boards or between floor boards, as shown in the photo below. Cold air will seep into the room from the garage below through these edge gaps. This will be true even if you have well fitted carpet in the room.

This thermal camera image below of a bare floor shows how cold air enter a room where there is no floor covering. The blue areas are cold air coming through from underneath.

Draughts through floorboards
Courtesy the Cheese Project Bristol

This thermal image shows how draughts infiltrate at the edges, even though the gap is very narrow. A 'gap is a gap' and air will find its way through!


Action 1 - Fixing the draught gaps at room edges

This was something I did on a problem floor of my own a few years ago. It made a big difference. After I did this the room stayed far warmer after the heating had switched off.

Even if you choose to use any of the other methods for addressing this problem I personally would always do this job.

This is a pretty simple DIY job and also very cheap (under a tenner). In my case I had very big gaps at the edges of the floor area and the room was never warm before I did this.

The gaps I had at the edges were quite large. So, to draught proof the edges I pushed some old newspaper into the gaps with a wallpaper scraper blade (as you can see the photo below). This alone does a pretty good job of filling the gap and keeping cold air out.

If your gaps are too narrow to squash newspaper that is a bonus! You can go straight to the next sealant stage below.

The next stage is to use a flexible sealant to seal over the newspaper that has been wedged into the gaps.

Newspaper will do a great job on its own, but it will help further if you use a flexible to completely close off the way for cold air to get through. This will also leave a more attractive finish.

This inexpensive decorators caulk is a perfect sealant for the job. You'll need a sealant gun to extrude the sealant and if you don't have one, get one of these. If you've never used a sealant gun, this 2 minute YouTube video explains how. There are other YouTube videos on using sealant guns if this one doesn't give you enough confidence to have a go.

The sealant is simply squirted into the gap as shown below.

If you find the sealant is going everywhere, don't panic, just reduce the pressure on the trigger to reduce the flow. The sealants suggested above can easily be cleaned up with a damp cloth.

(Please excuse the state of the floor and skirting board in these photos. This skirting board is inside a built-in wardrobe at home that we've yet to decorate!)

Smooth over and squidge the sealant in with a finger. If the carpet grip rods are in the way, use the wallpaper scraper shown above to do this rather than your finger, so you avoid the sharp pins on the grip rods.

This YouTube video is of a wonderfully cheery Australian lady showing you how to use the sealant gun. She doesn't use newspaper but uses a product specifically made to do the same job. Everything else is the same as my method above.

If messing about with sealant to seal the edges isn't for you here is a plastic strip product you can use as an alternative.

Lifting carpets to allow you to do all this

To do the above you will need to lift the carpet at the very edges of the room.

There are very few YouTube videos on how to lift a carpet, but here is one that at least shows you how to get going.

It may be necessary to lift the carpet grip rods if they're too close to the skirting board to do the job. The pins on grip roads are wickedly sharp so beware. Grip rods can easily be nailed back down if do you have to remove them.


Action 2 - draught-proofing gaps between floor boards

This action requires more effort.

Here we use a similar sealing method to the one I used above. In this case it is to seal the gaps between the wooden floor boards themselves. These gaps can be really wide in some houses.

This means gaining access to the floor area itself.

Depending on the room shape and size and how much furniture it contains, you might be able to complete this task without emptying the room.

The ideal is situation is if you can move furniture around and lift the carpet one part of the room at a time and do this job in stages.

Emptying the room completely and lifting the carpet is obviously more effort but might be necessary in some situations.

In my experience, if you lift and refit a carpet yourself, they refit reasonably well though never look quite as stretched and flat as when they were originally fitted.

Use plenty of sealant to fill gaps between the boards.

For these cracks I recommend a different sealant. one that is generally called a "frame sealant". It's applied in the same way as decorators caulk above but is more durable. Here is an example product.

If you have large gaps between floor boards you can always partially fill the gap first with newspaper just as I showed in Action 1 above. Partially fill big gaps with stuffed newspaper to reduce the amount of sealant you need to use.

Be prepared for some ugly sights though when you lift carpets in older homes.

The images below show the sort of draughty gaps that can lurk beneath carpet. A little DIY creativity is required to fill.

Cardboard or a thin piece of plastic can be cut to fit cover the gap and stuck in place would probably do. Whatever you do, it doesn't need to be particularly strong - just whatever works well enough to cover the gaps/holes and keep the cold air at bay.

An example solution - this takeaway container lid can be cut to size and shape to fit around the pipe and then stuck down with sealant.

If you have an access hatch to the crawling space below, it is important to make that as draught proof as you can.

Alternative method to filling gaps between floor boards

If using sealant to fill floor board gaps feels a bit too messy then here are some other options:

Stopgap product - This is a flexible plastic strip that you cut to size and fit by hand.

It is very quick to use, but more expensive solution, at around £25 a roll. You can find it here on Amazon (and you will probably need more than one roll). Here is the manufacturer website. It includes a a short video which explains how to fit the product.

The advantage of this solution is no mess, and you can put floor coverings straight back down although in my opinion it won't seal as well as sealant.

Draughtex - This is a rubber product that you insert into gaps. It comes in variety of thicknesses for under £30 for a 40-meter roll. More info here.


Action 3 - upgrading to highly insulating underlay and carpet

The choice of floor covering in the room above the garage can make a BIG difference to how cold a room above a garage will feel.

Carpet and underlay CAN provide very useful layers of insulation and can significantly improve comfort in the room. The insulating properties of carpet & underlay vary widely.

We are probably all familiar with the TOG system used for duvets to tell us how warm they are going to be. Higher TOG duvets are much better insulators than lower TOG duvets.

The carpet and underlay industry use the same TOG system to tell you how good an insulator carpets and underlays are. The higher the TOG, the better insulating the carpet or underlay is.

Carpet underlay

The traditional green rubber underlay you see here have a TOG rating of less than 1.5.

Compare this with a summer weight bed duvet, which typically has a TOG rating of 4.5.

This tells us very clearly that this underlay isn't going to be good at keeping the cold out.

There are many budget underlays that are even poorer.

TOG information is easy to find in product information when searching for or buying underlay.

If you have a thin or low TOG underlay you could invest in one with a HIGHER TOG rating.

There are many to choose from with TOG ratings as high as 3.6, This is much more like a summer weight bed duvet.

The best I’ve found, and one I have used in several rooms myself, is one made from 100% recycled wool (example shown below).

This type of insulation has been around for many decades, is very eco-friendly and hard wearing. It also has excellent sound insulation properties and feels lovely under foot. The thicker the better. These types of underlay can be as thick as 18mm and are typically cheaper than modern synthetic underlays.

There are numerous manufacturers and sellers online with very similar products but here is one example.

Working out the TOG rating of your existing underlay

You probably won't know the TOG rating is of your existing carpet underlay do you won't know if it is worth upgrading it.

It might not be too hard to identify though. The Carpetright website has a big range of underlays with good pictures of each one and associated TOG information.

If you lift a corner of the carpet and look at the style and thickness of your existing underlay. Take a photo of it, measure the thickness and see if it matches any of the products on the Carpetright website.


Carpets TOG ratings also vary a lot ranging from 0.7 to 3 TOG.

So, to give you a better insulated floor, it is possible to have carpet of 3 TOG on top underlay of 3.6 TOG. Add the two figures together and you have a total TOG rating of 6.6 for your floor coverings, much better than a summer weight duvet.

This will not be as good as having a properly insulated garage ceiling. In my experience though it should give a noticeable improvement if you currently have low TOG value floor coverings.

Upgrading to a higher TOG carpet is obviously a costly step. It might be something you keep on hold as an idea consider when you next replace the carpet anyway. The highest TOG carpets are likely to be wool carpets which are usually the most expensive.

If you currently have laminate flooring

Laminated or wood flooring is a poor insulator. High TOG carpet and underlay are clearly going to be much better. Or, at the very least, put thick rugs down where you commonly stand or sit.

Working out the TOG rating of your existing carpet

Identifying the TOG rating of your existing carpet might be harder than identifying the TOG of your existing underlay.

You'll have to do some legwork and visit a carpet showroom to look at different carpets, their TOG values, and compare to yours at home to work this out.


The best solution - insulating under the floor boards

There are several ways to do this, but the options you have will depend on how much space you have under the floor, laid out in the sections below.

The result will be around 5 times better than the carpet and underlay suggestions REALLY good.

Important safety points if you do any of the following DIY solutions

If you have any electrical cabling under the flooring you intend to insulate, it is incredibly important to understand what those cables do. In some situations, especially in the case of high-power cables (such as cables for cookers, immersions, storage heaters, showers) it may be important to keep insulation away from these cables altogether to avoid any risks of them overheating. If you are in any doubt, seek the advice of a qualified electrician.

Follow any guidance on the insulation product you use about the need to wear goggles or a face mask.

Ensure any central heating pipes underneath the floor boards are well insulated to prevent freezing.

Do not block any vent bricks. These are essential to prevent the floor timbers from rotting.


Insulating the floor if it is NOT possible to crawl underneath

This is the most difficult situation. If there is not enough height in the space underneath to crawl, you have two options:

Option 1 - lifting the flooring and insulating from above

This method means lifting all the floor boarding and fitting insulation between the floor joists from above.

This is obviously very disruptive, but the plus side is it is not actually very expensive to do, maybe £200 a room.

The floor boards can all be re-used too of course. If you've never lifted floor boards see here and here for some YouTube videos of how to do so quite easily.

This webpage also has a good written guide with diagrams on this method of insulating these floor from above.

This YouTube video also gives you a very practical insight in to how to do this whole job.

Option 2 - robotic spraying of foam insulation from underneath

A clever British company called q-bot has developed a small robot specifically for this job. It travels around the crawling space below and applies spray foam insulation to the undersides of the floor boards above.

It sprays a type of foam called 'open cell'. This is an extremely good insulator but also allows the floor timbers to breath.

This is a very effective insulation method, though is not cheap. The q-bot website is here.

Before and after

Insulating the floor if it IS possible to crawl underneath

If you can physically crawl in down there, then again there are two options:

Option 1 - insulate the underside of the flooring from below

This method means doing roughly the same as the Option 1 in the section above, but doing the job from underneath. This is obviously much less disruptive but is a pretty grotty job.

There are plenty of companies out there who will do it for you but it is possible to do as a DIY job which will be much cheaper.

This website gives a very good step by step guide on how to do it if you want to do it yourself, with a very honest view of the challenges of doing it this way.

Option 2 - use a specialist spray foam contractor

There are a number of companies who offer this as a service if there is crawling headroom of 0.5m or more to allow the spray to be added manually.

One of my neighbours had this done and they described it as 'transforming' the comfort of the room.

Similar to the robot application above, they use an open cell breathable type of spray foam. This is one of the companies who offer this service.

I believe the costs of doing this are in the range of £30-35 per square meter (March 2023).


Installing smart air bricks to control ventilation intelligently

Air bricks are essential to prevent mould and damp issues building up underneath suspended timber floors and prevent timbers from rotting.

But, traditional air bricks are quite crude. They are open permanently regardless of how much ventilation is actually required for the weather conditions.

A company called AirEx has developed a smart air brick that opens and closes automatically, in response to temperature and the humidity levels.

The AirEx smart air brick installed

They talk to a wireless control hub in the house. The system ensures that the vents are open only as much as they absolutely need to be.

This means that the space under suspended floors will generally be warmer than it would have with conventional ventilation. Draughts into the house will also be reduced when the vents are closed.

I believe the installed cost is somewhere in the region of £150 per vent.

They are powered by an internal battery lasts 5 years and can be changed by the homeowner. The central hub provides alerts when batteries need replacing. If a battery goes flat, the vent stays permanently open to guarantee ventilation.

For more information see their web site here.


I run this website as a hobby, because I care about this stuff, and do it for no commercial purpose. If you have valued the information here, please tell other people about it.

If you have any other suggestions for additions to the above, or would like to subscribe to email updates, please let me know using the contact form.



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