What are the regulations for floor joists in loft conversions?

What are the regulations for floor joists in loft conversions?
Why do you need to install floor joists in your loft conversion projects? What are the regulations for floor joists? Learn here! 

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A loft conversion project is an excellent and cost-effective way to obtain an additional living space. However, you need to follow the building regulations to ensure a seamless process. Research shows that homeowners need a great deal of care when dealing with an existing building. 

The existing ceiling joists are usually not suitable for use as a floor. Therefore, it is wise to install new floor joists to ensure extra load-bearing in the living space. Here are regulations for floor joists in loft conversions. Read on! 

Size of Floor Joists 

If you install 47 x 145mm joists at 400 mm centres, they must span up to 2.89m. Likewise, the 47 x 170mm joists installed will span up to 3.38m. If the contractor installs 47 x 170 mm joists at 400mm centres, they will span up to 3.38m. 

The installation of 47 x 195mm floor joists at 400mm must span up to 3.87m, and for 72 x 145mm (3.33m), 72 x 170mm (3.89m), and 72 x 195mm (4.44m). It is crucial to choose the right size joists for your floor to maintain structural integrity and meet building regulations. A structural engineer can help in this regard. 

100mm Wool Insulation between Joists 

UK law requires homeowners to install 100mm wool insulation between joists for sound insulation. Bear in mind that your existing ceiling may need upgradation to provide fire resistance if it is not 12.5mm plasterboard. 

In addition, traditional plaster or lath ceilings will achieve about 20-minute fire resistance. Therefore, it is crucial to comply with building regulations and upgrade the insulation by installing a layer of 12.5mm plasterboard to your ceiling. You can also install a mesh between and over joists with tightly packed wool insulation between them. 

Install Larger Floor Joists than the Existing Ones 

Because the existing ceiling joists can’t support your loft conversion loads or weight, it is crucial to install new floor joints to take these loads. Make sure you place these joists between the existing ceiling joists. Remember, the new floor joists you choose must be larger than the existing joists. 

The existing walls can support new floor joists if they are adequate. Otherwise, you have to focus on steel or timber beams for additional support. Make sure the steel or timber beams are adequately provided with fire resistance. Discuss the floor joists with the structural engineer you have hired for the project to ensure you meet the regulations. 

Final Words 

Floor joists provide additional support to your new living space. Experts recommend adding robust and larger floor joists between the existing ceiling joists. Besides, support them on the current walls, and you can even add in extra timber if needed. 

Remember, loft conversions design professionally comply with building regulations and rules established for floor joists. Floor joists strengthen your loft and add to your safety. At the same time, they are in accordance with UK’s building regulations. 

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