Level thresholds - landing and drainage

Blog Post
Level threshold diagram

Getting the design of a level threshold right can be tricky. Convenience and accessibility are the main focus, but this can cause water penetration or damp. The external landing should be large and level enough for easy wheelchair access, but there’s a risk of standing water or surface water reaching the threshold.

Here’s how to get the external landing and drainage right

  • Install an external landing with a fall of between 1:40 and 1:60.
  • Ensure water falls away from the doorway in a single direction, and make sure there are no cross falls.
  • Build a drainage channel between the landing and the threshold.
  • Ensure the channel discharges to a drainage system or permeable field drain.
  • Provide further drainage if the threshold is likely to experience extreme weather conditions.
  • Install a drainage channel at the junction of the ramp and landing to avoid ponding and any storm water reaching the threshold.

Where you’re dealing with low-lying or steep slopes, you need to prevent drainage channels flooding by installing additional drainage to adjoining land.

  • Construct the drainage channel as a site-formed slot above a discharge channel or by a proprietary drainage channel.
  • Ensure drainage slots are no wider than 18mm.

If your customer hasn’t factored it in, recommend additional measures such as a canopy roof to shelter them from rain.

Further information

Follow this step by step guide on level thresholds to ensure you comply with the Building Regulations and the LABC Warranty Technical Manual. View our upcoming drainage training courses.


(No subject)

Submitted 12 months ago

From the drawing, there appears to be no method of draining the cavity below the threshold or any protection to the insulation at this point. I would normally place a stepped DPC from the floor membrane down to the concrete cavity fill with weep holes in the outer leaf discharging into a bed of granular material surrounding a perforated land drain.

Webmaster note

Submitted 12 months ago

All comments posted at an earlier date to this one have been transferred from our old website.

Add new comment

This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

Sign up to the building bulletin newsletter

Over 48,000 construction professionals have already signed up for the LABC Building Bulletin.

Join them and receive useful tips, practical technical information and industry news by email once every 6 weeks.

Subscribe to the Building Bulletin