The perfect treehouse

Building a treehouse requires imagination, enthusiasm and some amount of DIY know-how. While  more complex structures need the input of an experienced designer, it’s always good to know the rules before you embark on such a project. 

 

Treehouses are among those unique structures that can spark, and feed, the imagination of adults and children alike. For grown ups they often evoke an ‘idyllic childhood’, real or imagined. They also offer the tantalising prospects of off-grid living, a retreat in a calming environment of dappled sunlight and shade. 

For children they are truly magical spaces that encourage their sense of adventure and play.

In recent times, treehouses have been used as everything from a traditional play space to a long-term residence, from the office to the hotel or restaurant, from therapy clinic to recording studio.

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Planning restrictions 

For planning permission, ROI local authority websites should give the relevant requirements (you can ring their planning office if there is no information confirming what they are). For example Dun Laoghaire Rathdown County Council outlines theirs as:

‘You can build a shed, (treehouse), etc., as long as… it does not extend beyond the building line of the house and does not exceed 4m in height, (if it has a tiled or slated pitched roof), or 3m (if it has any other roof type); the floor area limitation for exempted development is 25m²; it is not lived in’

Similarly in NI the government planning information website states that:

Planning permission is not required provided:
1. The shed / (treehouse) is used for domestic purposes only.
2. The ground area covered by the shed/ building and any other buildings within the boundary of the property, excluding the original house, is not more than half the total area of the property.
3. No part of the shed / building is in front of the principal or side elevation of the original house that faces onto a road.
4. The maximum height of the shed / building is 4m.
5. The maximum eaves height of the shed / building is 2.5m if it is within 2m of the property boundary.
6. No part of the shed / building is within 3.5m of the boundary with a road to the rear of the house.

Of course, in both cases there are further requirements on the location of windows, listed buildings, heritage sites, etc. However, unless you’re building a grounded treehouse (on no more than 1m posts) probably the most relevant item with regards to needing planning permission is the height restriction of four metres. Regulations aside, you will of course want to locate the treehouse with consideration of your neighbours’ privacy (including overlooking their garden).

In terms of building regulations refer to the Technical Guidance Documents for ROI and Technical Booklets in NI.

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The plan
In all cases you will need to draw up at least a basic design plan of your treehouse, considering firstly any possible locations available to you, and then the three main elements of the structure: platform, access and the building.

If you have a tree or trees which are suitable and large enough, and are going for a genuine treehouse you must first carefully consider the location. Should it be in one tree (with or without support posts to the ground) or possibly suspended between two or more trees. While a single tree may at first appear the easiest option, it does tend to lead to the tree trunk and possibly some of the main branches being left to grow through the structure and thus to more complex structural detailing. 

The two tree, or tree and posts, options allow you to position the building on a less obstructed platform. In this case you will also need to build in provision for wind movement between the two trees, with sliding brackets on one tree. With regards to security, particularly for children, carefully consider the location of the treehouse, positioning it close to, and visible from, the house.

The health of the tree(s) should also be determined at an early stage.

As to the style of the treehouse, literally anything goes. In recent years treehouses have been designed across the world as anything from simple canvas cocoons suspended in a tree in California, to a near invisible mirrored cube in a Swedish treehouse hotel, and everything in between. 

So be creative and use your imagination; you will however have to balance that with your budget, time and other resources available to you. Don’t take on building a dream children’s treehouse that won’t be finished until they are in their teens. 

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Platform and access
Begin your design with the platform, which will, in most cases, be made up of two or more main bearers across which are laid the joists, then finally the decking or flooring material. Any required knee-braces, struts or support posts should be included to create a safe and stable base on which to build your treehouse. Depending on the complexity of the design you may at this stage need to engage a structural engineer to sign off on your specifications. The final decking /flooring material must be cut back sufficiently to allow for growth/expansion of the tree trunk over time. 

The health of the host tree must also be taken into account, with the minimum pruning necessary to facilitate the treehouse, and the support designed with a balance of safety and the minimum of individual fixings through the outer living cambium layer of the tree trunk. This can be done using heavy-gauge coach screws (or lag bolts) along with custom-made galvanised, or better yet, stainless steel brackets. A wide range of proprietary treehouse support fixings available online from the US can be purchased by Irish treehouse builders. 

In order to ensure that the overall stability and safety of the structure does not rely on a single component or support member at any point, a fail-safe system should be considered.This involves braided steel wire looped through a point above the treehouse that is attached to the ends of the main bearers. 

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The house
You can now design your actual ‘house’, depending on the type of treehouse you want and its purpose. Keep in mind the longevity, and possible adaptability of the structure to future uses. For example a children’s play house could in time be adapted as a den and study room after a few years and a more adult space after that.

As previously mentioned, the range of materials you can use is practically limitless. With that in mind, but sticking to the more conventional for the present, you need to decide on the level of specification for the build. For example, should the structure be insulated; what standard of joinery do you want (single or double glazed, softwood or hardwood windows and doors); should you include power and light? A good quality slate or cedar shingle roof will protect your structure for many years. At the very least all timbers used in the treehouse, platform and access structure should be pressure treated softwood.

Usually the wall structure would be 100x44mm pressure treated studwork with 100mm rock wool insulation and a breathable membrane externally. The exterior would then be battened and clad in any one of a number of timber finishes, such as horizontal or vertical boarding, ship-lap boards or cedar shingles. The interior finish should be some form of timber sheeting or panels. Never use a plastered finish; it will crack as the structure moves. 

Similarly with a pitched roof, the rafters should be a minimum of 150x44mm treated timbers with collar ties (to prevent spreading or even collapse), then add insulation and internal finishes as for the walls. The roof finish could be slate, cedar shingles or corrugated iron sheeting, depending on budget and taste.

Lastly, you should consider access and safety, taking into account who will be using the treehouse. If it’s for children keep the platform lower or at least break the climb up into safer, more manageable stages. Access will be via one or more of three basic methods: 

A staircase is generally set between 20-40deg from the horizontal, a ship’s ladder between 60-75deg with handrails, and a ladder between 75-90deg without handrails. 

Rope ladders can also be used but only as a secondary means of access as some children or adults will not be comfortable using them.  

 If you’re lucky enough to have a tree on a sloped site, a bridge from a point on the adjacent slope may be an option.

In an urban situation, where no suitable tree is available and overlooking may be a problem, it can still be possible to work in a structure that can achieve the feel and sense of a treehouse, by raising it off the ground and adding a tree within the structure.

Having designed your treehouse, there are any number of features and accessories you can add on at this stage. These include:

  • Crow’s nest
  • Swings
  • Slide
  • Zip line
  • Hoist (basket and pulley) Climbing wall or net
  • Trap door and rope ladder
  • Water cannon (hose on spindle)

Last but not least it will be important to estimate the total combined weight of the materials, and potential number of occupants, before you complete your design, in case it needs to be altered; e.g. so as not to overload the support trees, or to check whether additional supports are required. Wind and snow effects will also vary with height, exposure and the profile of the structure.

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The build
Once you have your design and planning sorted out, prepare a materials list and get it priced by two or more suppliers and joinery workshops. Be methodical with your build. Write out a work schedule and arrange help as you need it. Prepare your work site. Give yourself a generous amount of un-cluttered space to work in. When you take delivery of your timbers, set up a storage rack of three or four timbers on concrete blocks, sort and neatly stack them (preferably in order of use) and protect from the weather with heavy gauge polythene. Uncovered, unsupported and loose timbers will warp and twist in a matter of days. 

You now should treat your work area as you would any building site: 

  • Cordon off with temporary fencing and keep the work area tidy and safe.
  • Wear safety boots, hard hat, hi-vis vest and work gloves. 
  • Never work alone, particularly when above ground. 
  • Be alert to people below you when working at a height.
  • Use a safety harness, looped through the tree canopy, when working at a height.
  • Use only cordless or low voltage power tools.
  • Where temporary access is needed, use a heavy duty extension ladder tied securely at the top (on the tree).
  • Use a well-supported scaffold tower if required.
  • Never use a step ladder.

At this stage stand back and look at your tree carefully. Prune out any timbers as previously decided, also remove any dead or damaged branches, particularly from the tree canopy above. 

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You are now ready to build. Start with the platform, providing temporary support as needed until it is complete and the final supports are in place. Next build your stairs or ship’s ladder to provide a safer and more comfortable access point to the work platform. As much as possible pre-fabricate your walls at ground level and assemble them in manageable sections. 

You will now need several strong helpers on site to lift the panels into place using a rope and pulley system rigged from the tree canopy above. For safety, fit posts and handrails to your deck as soon as possible. Construct the roof and seal around the tree as necessary using metal flashings and a flexible butyl rubber collar. Fit out your windows, doors and interior, installing electrics as and if required. Finish any detailing and fit any accessories as planned. Finally, clean up and re landscape your work area. 

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Final word
For safety and to get the best from your treehouse, check the structure regularly, particularly after stormy weather. Pay special attention to metal fixings and brackets, also handrails, support posts and timber bracings. Tighten up or replace fixings as required, similarly with structural timbers. Examine the tree canopy above and prune any dead or decaying branches before they become a hazard.  

Disclaimer: This article is a guide only and does not purport to replace expert advice; always consult an experienced designer to ensure the structure you build is safe and complies to the relevant regulations. ν

Peter O’Brien MGLDA

www.planeden.ie

Additional information: 
Les O’Donnell, 
79 Botera Road, Corlea, 
Omagh, Co Tyrone, BT78 5LQ, 
tel. 8224 1831, mobile 07784 573 222, 
www.landmarkdesigns.org.uk

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About Astrid Madsen

Astrid Madsen is the editor of SelfBuild & Improve Your Home magazine. She previously held the same role in an Irish trade publication, before that she worked at the National Standards Authority of Ireland. She graduated with a BA in Urban Studies from Columbia University in New York and holds an MBA from the Instituto de Estudios Bursatiles in Madrid. France of origin, she now lives in Portarlington, County Laois, where she's taken on the task of renovating a listed building! Email astrid.madsen@selfbuild.ie

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