Building Near a Protected Tree:How Close Can You Go?

Most of a tree's roots grow in the top 600mm or so of soil, and they often spread well beyond the edge of the canopy. Digging foundations, laying a slab, trenching for drains or raising the ground level can cut or suffocate them.

The damage often shows years later, as dieback or instability. Under a Tree Preservation Order, wilfully damaging a protected tree, roots included, needs the council's consent in the same way felling does.

BS 5837:2012, Trees in relation to design, demolition and construction, is the standard councils use. It sets a root protection area (RPA) for each tree:

• Measure the trunk diameter at 1.5m above ground.
• Multiply it by 12. That's the radius of the RPA.
• So a tree with a 50cm trunk has an RPA radius of 6m.
• The area is capped at 707 square metres, a radius of 15m.

Trees with several stems use an adjusted calculation, and an arboriculturist can change the shape of the RPA to reflect the site, for example where an existing wall or road has limited root growth. Treat the simple circle as a starting point.

If you need planning permission, most councils expect a tree survey to BS 5837 where trees on or next to the site could be affected. For a build near a protected tree, that usually means:

• An arboricultural impact assessment, showing which trees are affected and how.
• A tree protection plan, showing fencing and ground protection around each RPA during the build.
• An arboricultural method statement, setting out how any work inside an RPA will be done.

A full planning permission can authorise work to a protected tree that's necessary to carry out the development. Permitted development rights don't. If you're building under permitted development, any work that would damage a protected tree still needs TPO consent.

Building inside an RPA isn't always ruled out. Common approaches include:

• Pile-and-beam or screw-pile foundations that bridge roots rather than cutting a trench.
• No-dig surfacing for drives and patios, laid on a cellular base above existing ground level.
• Hand-digging and rerouting services around significant roots.
• Moving the footprint so only a small part falls inside the RPA.

On shrinkable clay soils, nearby trees also affect how deep foundations must be. Building control and warranty providers have their own rules on this, so raise the tree with them early.

1. 1Check for TPOs on the property and on neighbouring land: a neighbour's protected tree can have roots under your plot.
2. 2Check whether you're in a conservation area.
3. 3Measure the trunk and sketch the simple RPA on your site plan.
4. 4Talk to the council's tree officer before you finalise the design.
5. 5Commission a BS 5837 survey if you're making a planning application.