Floors

Floor Cassettes

Where possible we design our floors as cassettes. This allows for easier onsite construction and for a quicker erection. As the material is sent as cassettes rather than bundled loose items the construction site is cleaner and easier to manage – thus ensuring high standards of Health and Safety, Construction Design Management and site management. It also creates an environment where accurate construction can be ensured and monitored.

Typical Details

If the floor is an I-beam floor then the depth of the floor joists will depend on the engineering. Typically OFP timber frame work to 240mm, if the floor is solid joists then the minimum depth of the joists can be 220mm. This is to robust details E-FT-1 and EFT- 2.

Blocking used in cassettes varies depending on the detail specified by the engineer. Typically, on an external wall the floor will only require I-beam blocking. On internal walls a 45mm Kerto-S blocking will be required for fire and sound regulations. See below for Finnforest standards (available in the Finnframe Brochure at http://www.finnforest.co.uk/).

When designing transport blocking for cassettes we adhere to Building Regulations Approved Document A, Table 3 ‘Strutting to Joists.’ Although this is only strictly necessary when a floor is engineered to 14mm deflection, it is a good rule of thumb for cassette design.

To close off cassettes there are a number of options available depending on how the cassettes sit; whether it is on an external wall, internal wall or hanging off a beam. If the cassette sits on an external wall the cassette will be closed with the Kerto-Q rimbeam. If the cassette sits on an internal wall or hangs off a beam, a line of blocking 300mm from the end of the cassette can close off the cassette. (See diagram below).

Rimbeam is typically 33mm Kerto-Q at the same depth of the floor joists. However, the engineer may specify a 39mm or 45mm Kerto-S rimbeam if disproportional collapse is required.

Decking to flooring in flats is 18mm and in a house is 22mm. For flats roofs we use 12mm WBP ply and firings if required.

When designing floor cassettes we try to keep them as a square shape, any timbers on an angle and all timbers connecting to the angle timber will go to site as loose material. A 600mm tolerance gap is left between each cassette; this will be filled on site with the relevant noggins and rim board.