Part 2 - Types of UFH for joisted floors
So you’ve read the The Golden Rules for joisted floors with UFH, and you’ve seen lots of marketing about systems claiming to be easy to fit. But, how do you know what type of system is best for you as the installer, and what will deliver for your customer?
There are many types of system available, some more suited to new-build, some for renovation. Some add a lot of height, but at least one (OneBoard® by Continental Underfloor®) adds only 4mm of extra height (yes, just 4mm, and we're proud of that!).
So what are the options for joisted floors and underfloor heating? At this stage I hope you will excuse me for focussing on Continental Underfloor® products; because with the widest range in Europe, coupled with 20 years’ experience of tens of thousands of systems, they have a fair bit of expertise.
By far the easiest and simplest way to fit UFH on a new-build joisted floor is to plan early, and build it in early, by using the Continental Underfloor® OneBoard® system. This is a 22mm structural floor system, fully tested by TRADA. It replaces the normal 18mm chipboard or ply that is typically laid on top of joists.
The unique design of OneBoard® means it can be laid herringbone, as you would for normal 18mm decks. There are no complicated “return” panels to worry about, and the small additional height increase (4mm) can be easily accommodated. There are copy-cat products out there (such flattery), but for a structural deck, you need it to be a tested product that’s been proven in action.
I have health & safety reservations about these being used between joists, as I mentioned in Part 1. However, they do have their place, despite being “old-tech”. Another way to fit them is between battens laid on top of the deck (but you will get a height increase).
And let’s not forget the “old-tech” version (thankfully being superseded) which involves fitting the plates into grooved insulation panel before piping up. According to installers (and my own experience), this is a right old palaver that’s thankfully being consigned to history.
There is a misconception that thin plates don’t conduct as well as thicker plates. You’ll see “detailed” proofs on some websites claiming their 0.Xmm thick plate performs better than any other. In reality, the difference is small, and the bigger issue is how easy the plates are to use and fit.
Beware of very thin plates (0.4mm and below), primarily because they are hard to work with and install, flexing all over the place and creasing. Really thick plates (greater than 0.7mm) also have their issues including, in our experience, a greater risk of squeaking as they heat up. No customer is going to thank you for that...
The AluPlate™ range by Continental Underfloor® includes a well priced “trade” version, as well as the premium product that includes our QuikSnap™ technology. This greatly speeds up installation.
You’re doing a renovation and the final floor is already laid. Then, the customer decides at this late stage that they want UFH. If you can get access from below, Continental Underfloor® has the unique “fit-from-below” AluPlate™.
It simply screws into the underside of the deck and the pipe is pushed in.
No fit-from-below system is easy to fit, but they provide a solution when no other options are available; and believe me, I have tried many over my 20 years in the industry. The Continental Underfloor® FFB AluPlate™ is the simplest I have found, which is why we sell it.
Once the floor deck is laid, the options are reduced. There are many systems on the market for “over floor” situations. Some are better than others, and some are downright appalling. First, they all have minimal insulation so there needs to be additional insulation installed below the floor deck. If someone claims their thin system provides all the insulation you need, then run away quick: they don’t have a clue.
Some overfloor systems require two panels: a return panel for the edges and a straight-run panel for between. At Continental Underfloor®, we lead the market with the innovative SlimFix®, which is a single-foiled composite panel system with the returns built in.
Of course, others have copied us since. This is the height of flattery, but a lot of the copy-cats use low-grade “packaging” EPS, which breaks and flakes.
SlimFix® is now available for “normal” and “low temp” use. There’s a “trade” version, and heavier duty panels with a huge 500kPa compressive strength, available in 18mm or 25mm thicknesses.
With systems such as SlimFix®, you can generally lay a wood floor direct onto the panels, subject to the rigidity and thickness of the wood floor. Again, the expertise and experience of the specialist supplier really counts here.
The problems with all foiled overfloor systems occur when it’s time to tile over them. It is possible, but special preparations are required with primer and specialist adhesives, and there are consequential long drying / curing times. Alternatively, they need covering with ply or a screedboard. All this extra work adds cost and takes time, and can throw the build schedule out by days.
It’s for these reasons that we developed TileFix®, our unique specialist overfloor system. TileFix® simply fits down and can be directly tiled over using normal flexible adhesive: no primers, no wood covering, no curing time, no hidden costs, and no delays.
To prevent the tiles and tile joints cracking, TileFix® has a super high compressive strength of 500kPa – heavy industrial grade. By contrast, most overfloor panels systems range from 100 to 300kPa compressive strength, which is why additional ply layers are needed on top.
TileFix® is a companion product to SlimFix®: you use SlimFix® where you have wood floors or carpet, and TileFix® for the tiled areas. TileFix® also comes in “low temp” and “normal” versions; and like its sister product, comes in 18mm and 25mm versions.
Another interesting result of having specific products for different types and thicknesses of floor cover, is that gaining a level final floor finish becomes a lot simpler. For example, the thinner 18mm SlimFix®-18 would be used for the wood floor, with the thicker TileFix®-25 used for tiles, which tend to be thinner. This is where experience and expertise counts.
There are a few on the market that really perform, and Continental’s UltraSlim™-15 is one of them. This has our signature single composite board approach, and is suitable for wet rooms such as bathrooms.
But do you really have only 15mm to play with? Can you stretch to 18mm? Thinest is not always best, and our Technical Sales Advisers will give you an honest appraisal of whether it is right for your project.
Screed boards routed to take a UFH pipe have been around for a while. Typically, they perform well, are simple to lay, and provide good outputs.
Continental's ThermoDEK™ has a simple tongue and groove edge which makes it easy to align. These systems aren’t really economic for small areas (such as a single room) because their high density and weight is relatively expensive to transport, but for a whole floor or house, they are a winner.
Screeding over a timber deck is common in some European countries but isn’t really done in the UK. We are not fans of it, nor a batten and dry-mix system.
The bottom line is that it’s a lot of work that negates any cost saving in the UFH system; however, for a self-builder providing their own labour, it can help reduce costs. Outputs are high, so they also have a place in hard-to-heat properties. Continental Underfloor® can advise you whether or not you need this approach.
With so many systems around that could be used with a joist floor, it makes sense to get expert advice early, from a company that has many different solutions.
Plan and fit the UFH early in the project, and it will be a simple way to introduce the luxury and efficiency of underfloor heating.
Don't think you can't use underfloor in a renovation project, because modern systems are manufactured for easy installation in a range of projects.
But please, get advice, and chose a reputable company. The system may cost a bit more, but you'll save time and have a happy, satisfied customer.
Author: Chris Ingram was the Chairman of the UK underfloor heating trade association for 8 years, and the founder (20 years ago) of what has become Continal® Group, best known in the UK as the trade specialist supplier Continental Underfloor®. Continal® design and supply across Europe, with Europe’s widest range of energy efficient underfloor heating systems. Chris continues to be Chairman of Continal®, and provides consultancy internationally to UFH suppliers, manufacturers, and suppliers. Chris has been responsible for some of the most ground-breaking developments in underfloor heating systems.