Loft Conversion Floor Joist Regulations

Loft conversions are functional, valuable home improvements that are generally much faster and more convenient to have installed compared to a traditional extension. With additions like terraces and balconies, en-suites and other design features, you can get a huge amount of space and use from this kind of investment. 

With the right loft conversion company, the whole process is all very well taken care of, with you remaining informed, but very much able to relax as the site manager stays on top of the project overall.

Importantly, though, it is helpful to understand some of the more technical aspects of loft conversions, as some of them can have large impacts on the potential for the build, and legalities in the planning process.

One key example of that is floor joists, and below we’ve got a really good insight into what they are, the regulations surrounding them, and how they impact a loft conversion project: 

Why Are Floor New Joists Necessary For A Loft Conversion? 

Across the UK the majority of homes (especially those with a pitch or cut roof) have internal support struts as part of the loft space to keep the purlins (horizontal roof beams) and rafters propped up.

It can slightly differ from other roof types, but there will always be similar types of support which are considered to be inadequate as floor joists, or as structures to be turned into floor joists.

For this reason, for a loft conversion to be done, new floor supports have to be created and constructed both above and below the loft space, and the original beams and rafters are then usually removed. 

Is It Always Impossible To Turn Original Support Struts Into Floor Joists? 

Most of the time, it’s not possible to turn support struts into floor joists when you are having a loft conversion done. Most of them are highly inadequate for the job, which becomes a little more apparent when you understand exactly what the job of a floor joist is. 

So, the support struts in place in a house without a loft conversion do a great job of supporting a roof. It’s an important job and a lot of weight to support, but that is very different to what they would be doing if you used them as floor joists.

If they remained in place in a loft conversion they would have to support the weight of furniture, extra insulation, walls, en-suites, new windows, and the weight and activity of people spending time in the converted space.

With that in mind, you can understand why the supports there are not suitable, and so, additional support is not only recommended but necessary to ensure the structural soundness and safety of the new loft conversion. 

Is It Difficult To Have New Floor Joists Added? 

When you use a highly trusted, expert loft conversion company, you can utilise the skills and abilities of both the building and management team, the design team, and structural engineers, all in-house. 

Structural engineers can check and assess the distance needed between floor joists to properly support the needs of the conversion. These floor joists will sit between the walls, usually above the joists already in position as ceiling joists (this method is called over-slinging), and can be 200mm to 225mm in depth depending on your needs.

If there is not enough room to do this and headroom is too compromised, side slinging may be done, which is where a special merge of new and old joists, plus holders and various other parts are used to create one effective support system for the floor. 

You may find that additional strength needs to be added, too, which would likely be in the form of timber or steel beams. With a professional construction company, you can trust that the safest option will always be the recommended option so that your conversion is functional, fit for purpose and completely safe. 

Loft Joint Regulations And Considerations

Your expert loft conversion company will be able to discuss loft conversion floor joist regulations with you to ensure that everything that is done is safe and structurally sound during the project. 

There are certain things they will likely need to consider when creating your design relating to the regulations, and they are: 

• Ensuring there is enough headroom available once the floor joists are placed (with side slinging as a second option to get around the issue or preserve maximum headspace)
• Using the correct thickness and positioning of joists in line with Building Regulation guidelines
• Including at least 100mm of insulation between joists for sound insulation

Additionally, there are some specific numerical guidelines your team has to consider, including: 

• Installation of 47 x 145mm joists needs to span up to 2.89m 
• 47 x 170mm up to 3.38m
• 47 x 195mm up to 3.87m
• 72 x 145mm up to 3.33m
• 72 x 170mm must be up to 3.89m
• 72 x 195mm up to 4.44m

These kinds of details are something a structural engineer will be more than aware of, and they will be including them in their designs to ensure that your loft is not only safe but stands in accordance with Building Regulations.

They will also be looking to include enough insulation in the roof to match a U-value of 0.16W/m2K minimum, but ideally, enough to better any present value so that the space is as energy efficient as possible. 

Speak To A Loft Conservation Expert For More Information

To find out more about your loft conversion potential, including the kind of floor joists you would need, speak to local, trusted loft conversion experts at Clapham Construction Service today.

They can discuss all the details with you, taking care of the technical bits so you can happily stay informed but relax in the knowledge the conversion you’ll get is safe, legal and strong.

Then all that’s left to do is decide how you’ll use it. Home office? Nursery? Guest suite? The possibilities are endless with such a transformative home improvement.