A Complete Guide to Underfloor Heating on Joisted Floors

If you’ve started looking for a new underfloor heating system and are wondering if you can get underfloor heating for joisted floors, this guide will give you all the information you need to make an informed decision. At UFH1, we specialise in providing underfloor heating systems for all flooring types, including traditional timber joists and modern floor joisting systems.

What Is Joist Underfloor Heating?

Joist underfloor heating is an underfloor heating system that has been designed to specifically work under joist (otherwise known as suspended joist) flooring. Joisted flooring is a type of floor construction that uses beams to support the floor's surface.

Joisted flooring is often found in older homes, but can sometimes also be found in new builds. Because of the structure of joisted flooring, you will need to find a compatible underfloor heating system that can be placed between the joists to prevent heat loss. 

If you want to learn more about underfloor heating for different flooring types, our expert guide goes through the best systems and installation methods for each floor type.

Can You Install Underfloor Heating for Joisted Flooring?

You absolutely can install underfloor heating for joisted flooring. However, you need to ensure you choose a system that is compatible with your joisted floor. Between-joist underfloor heating systems are specifically designed to work within the gaps of a joisted floor, making them perfect for both new builds and retrofit projects.

Underfloor Heating for Standard Timber Joists

Standard timber joists are generally 9” x 2” and spaced at 400mm, and are typically found in homes built since 2000. There are three options for installing underfloor heating alongside standard timber joist flooring. Here’s everything you need to know:

Insulation with Stapled Pipe and Sand/Cement ‘Biscuit Mix’

1. Wooden battens are fixed down the lengths of each joist at a distance of 100mm/75mm from the top of the joist. 
2. 75/50mm of foiled back insulation (such as Kingspan, Celotex etc.) is then fitted between the joists, being supported by the battens.
3. Remember to leave a 25mm gap between the top of the insulation to the top of the joist.
4. The pipes are stapled to the insulation, and then a sand/cement mix can be fitted to create thermal mass.
5. Please make sure with a structural surveyor that this method of joist underfloor heating is suitable, as the biscuit mix adds 20kg/m2 in weight.

Cross Battening Method

1. 2” x 1” battens are fixed at 400mm centres to create a ‘fake’ joist floor, leaving a 100mm gap at each end for pipe returns.
2. Once this is done, pipes are then nail-clipped to the subfloor, and an 8:1 mix of sand/cement is applied.
3. Chipboard flooring can then be laid and fixed to the battens, with the floor converting on top. A solid/engineered floor can be laid at a 90° angle to the battens.
4. Doing this raises the floor by upwards of 25mm from its original level, with insulation being pitted below the original level.

Aluminium Spreader Plates

1. For this underfloor heating system for joisted flooring, double groove aluminium spreader plates are fitted to the top of the joists with a pipe fixed to them. 
2. This method does not offer the same levels of thermal mass as previously described methods, and the aluminium plates can expand and contract, creating unwanted noise. This is because the pipes are spaced at 200mm centres, so we cannot endorse their use with heat pumps.

Underfloor Heating for I-Beam Joists

I-beams are common in modern timber framed homes, and the wooden flooring is sealed and screwed to the joists for rigidity as the home is built up. I beam joists cannot be notched, although they usually have ‘knock out’ holes in the vertical parts for pipes.

Cross Battening Method

This method is the same as previously described. Here is a brief overview:

1. A false floor is created with 2” x 1” battens that are fixed at 400mm with a 100mm gap at each end
2. Pipes are then nail-clipped to the sub-floor and an 8:1 sand/cement mix is applied.
3. Chipboard flooring can then be laid and fixed to the battens, with the floor converting on top. Solid/engineered floor can be laid at a 90° angle to the battens.
4. This raises the floor by upwards of 25mm.

Fit Underfloor Heating from Below

1. For this joist underfloor heating method, holes would be drilled into the I-beams, or pipe threaded through the ‘knock out’ sections and the pipe loop would be pulled into the length of each bay.
2. The pipe is then nail-clipped to the flooring above.
3. Once this is done, foil backed insulation is fitted underneath the pipes and suspended using wooden blocks or equivalent. There are also single aluminium spreader plates available for fitting from below.
4. Please note that this method of underfloor heating for joisted floors can be time-consuming.

Underfloor Heating for Eco Joists

Eco joists are ‘webbed’, almost ‘meccano’ like joists. Their webbing is ideal for routing plumbing pipes and cabling, so they are common in new build block construction homes. Eco beam joists cannot be notched, and it is difficult to fit insulation in between them because of their webbing. However, it is possible to install between joist underfloor heating with eco joists.

Cross Battening Method

This method is the same as previously described. Here is a brief overview:

1. A false floor is created with 2” x 1” battens that are fixed at 400mm with a 100mm gap at each end.
2. Pipes are then nail-clipped to the sub-floor, and an 8:1 sand/cement mix is applied.
3. Chipboard flooring can then be laid and fixed to the battens, with the floor converting on top. A solid/engineered floor can be laid at a 90° angle to the battens.
4. This raises the floor by upwards of 25mm.

Fit Underfloor Heating from Below

1. For this joist underfloor heating method, holes would be drilled into the I-beams or pipe threaded through the ‘knock out’ sections and the pipe loop would be pulled into the length of each bay.
2. The pipe is then nail-clipped to the flooring above.
3. Once this is done, foil backed insulation is fitted underneath the pipes and suspended using wooden blocks or equivalent. There are also single aluminium spreader plates available for fitting from below.
4. Please note that this method of underfloor heating for joisted floors can be time-consuming.

Why Choose UFH1 for Your Joist Underfloor Heating

At UFH1, we have years of experience and knowledge when it comes to fitting between joist underfloor heating. Whether you’re looking for a heating system for timber joists, I-beam joists or eco joists, we can help you find the perfect system for your project. Our customer care and technical teams are here to help with installation advice, system design, and aftercare, providing support from start to finish.

Find the perfect underfloor heating system for you, whether you’re looking for a retrofit or a new build. Or, if you would like more information on what underfloor heating actually is and its benefits, our blog on underfloor heating will provide you with everything you need to know.

Joist Underfloor Heating FAQs

Can you put underfloor heating on a suspended timber floor?

Yes, you absolutely can install underfloor heating for a suspended timber floor! There are several ways of doing so, including between joist underfloor heating systems, insulation between joists, cross battening or aluminium spreader plates. Choosing the best method depends on your floor type, spacing and whether it’s a retrofit or a new build. Reach out to us if you need more information on which underfloor system is right for you.

What is between joist underfloor heating?

Between joist underfloor heating is a system which involves fitting insulation and heating pipes in the gaps between flooring joists. This is a popular method of underfloor heating, especially in older properties which are more likely to have joisted flooring.

Which underfloor heating method is best for timber joists?

The best method of underfloor heating depends on the structure of your flooring and your usage needs. For example, cross battening gives excellent heat retention, while aluminium spreader plates are simpler to install but might not hold heat as effectively. For timber floors, we recommend systems that maintain insulation and avoid excessive weight. Have a look at our collection of underfloor heater kits to find the perfect one for your project.