Building safely

Treehouse Simulator helps you plan. It can’t see your site, your timber or your tree, so the checking before and during the build is yours.

What the app does, and doesn’t

Its sizes, spans, fixings and warnings follow published rules of thumb for garden structures and children’s play equipment (the sources are listed below). They’re a sensible starting point, not a structural calculation. They assume sound, correctly graded timber, firm ground, fixings fitted as described, and ordinary use.

Have anything load-bearing checked by someone qualified before children use it: posts, beams, anything fixed to a tree, bridges, and anything high.

Before you build

• Permission. Many raised decks, treehouses and garden buildings need planning permission, and larger ones building regulations approval. The app gives pointers for England, Wales, Scotland and Northern Ireland; check with your council.
• The tree. Ask your council whether it’s protected (a Tree Preservation Order, or a conservation area) before you bolt into it, prune it or dig round it. Have an arborist check that it’s healthy and big enough. Never fix to a tree that’s dead, diseased or leaning badly.
• The ground. Dig post holes by hand near trees, and move a hole rather than cut a thick root. Check for pipes and cables first.
• The timber. Buy structural timber graded (C16 or C24) and treated for ground contact (Use Class 4), as the shopping list says.

For children

• Height. Keep decks low for young children: as a rule of thumb, no higher than about 0.8 m for under-2s, 1.5 m for 2 to 5 and 2.1 m for 6 to 12. Help me choose sets designs to these.
• Guarding. Rails 1.1 m high round anything more than 600 mm up, with no gap a 100 mm ball could pass (under 89 mm round play decks).
• Soft landings. About 300 mm of play-grade bark chips under and round anything children could fall from, 1.5 m out or more. Never paving or concrete.
• Supervision. Young children need an adult nearby. Fireman’s poles are for children of 5 and over.

Building it

• Follow the makers’ instructions for fixings, brackets and bought parts (slides, swings, nets).
• Work at height from a sound platform or scaffold, not a ladder leaning on the tree. Get help with heavy lifts.
• Wear eye and ear protection when cutting, and seal cut ends of treated timber with the preserver on the shopping list.

Afterwards

• After the first summer, retighten every bolt and coach screw: the timber shrinks as it dries.
• Every spring, check for rot, loose fixings and splits, and top up the bark chips.
• Trunks grow a few millimetres all round each year: check the gaps round the tree and trim them back as needed.

Where the rules come from

The rules of thumb come from UK and international guidance, including: the Timber Decking and Cladding Association’s code of practice and decking handbook; NHBC Standards; the Building Regulations Approved Documents (especially Part K, protection from falling); EN 71-8 and EN 1176 on children’s play equipment, through published summaries; the US public playground safety handbook (CPSC Pub. 325); and treehouse builders’ and hardware makers’ published guidance.