YOUR BUILD: GOOD PRACTICE FROM START TO FINISH
STRUCTURAL STABILITY & ENGINEERING
A basic principle is that all buildings and structures should be safe for their inhabitants and regular users as well as the general public. Designers, builders and landowners on whose land these structures stand all have significant legal responsibilities in this regard.
In order to satisfy the building regulation requirements of Type 23A for structural stability (ie to meet building standard 1.1), either of the two following good practice options may be followed:
You may choose to follow one of the engineered models in hut types (and Appendices 1 and 2) in this Guide exactly - there is still plenty of scope for individuality in the choice of form, finishes and materials, fenestration, services and systems, cladding etc. as is made clear from the many areas of design covered in this Guide.
2) You may collaborate with a structural engineer to achieve your own or your architect’s hut design. Your engineer must provide you with a fully specified structural design for your hut and certificate for the design of both foundations and superstructure calculated in relation to the actual site conditions concerned. As long as you adhere to the 30 m2 rule (for maximum internal floor area) and all other mandatory Sections of this Guide, you will not need to apply for a building warrant. You could use the engineered models in this Guide as a point of departure for your own design, which could reduce an engineer’s input.
FIXED COMBUSTION APPLIANCES
Fixed combustion appliances include woodburning stoves, the most common heat source in Scotland’s huts. There are important health and safety standards for stove installation, which are designed to protect the hut and its occupants from fire risk, as well as from carbon monoxide poisoning, and these must be observed very carefully.
In order to satisfy the building regulation requirements of Type 23A for fixed combustion appliances (i.e. to meet standards 3.17 to 3.22 inclusive) your installation should conform to all the conditions set out in the heating part of this website.
ACCESS & ACCESSIBILITY
The ease of access to a hut is at the discretion of the hut owner. Some huts will be intended for people with disabilities and these will be designed accordingly. They may include a suitable access path from the nearest road.
It is envisaged that to maintain the low impact of hut developments, cars will often be kept remote from the hut site itself. Sometimes the provision of ramps (see decks) or level thresholds to doors (see Windows and doors) will be easy to achieve without additional expense and these are recommended as good practice.
Timber framed huts will often be raised clear of the ground with suspended floors and there will therefore be a need for steps. Sometimes a deck or walkway from slightly higher ground can be used to eliminate this need. In these cases, the mandatory regulations (see pedestrian protective barriers below) will need to be observed in relation to the height off the ground, edge protection and hand rails. (see also decks).
A hut can be little more than a camping shelter without services and without insulation, designed simply to keep out the wind and the rain. Or it could be a fully serviced, well insulated hut designed for year-round use. Wherever a hut falls on the spectrum between these extremes, it should exhibit a simplicity of form and materials and an economy of design - not least because this will enable it to fulfil the other expectations of sustainability, low embodied carbon and de-constructibility.
Simple does not necessarily mean traditional but there is much to recommend a simple orthogonal or rectangular floor plan and a constant short cross section.
LOW CARBON & LOW IMPACT
When designing your hut in compliance with Scottish Planning Policy, you will want to ensure your hut is as low impact as possible. The term ‘low impact’ is used to refer to developments which have little or no negative impact on the surrounding ecosystems, other natural systems (such as the water or atmospheric systems), or human activity and enjoyment of the area. The term can also be interpreted in the context of the Scottish Government’s ‘low carbon’ transition strategy. (“A Low Carbon Economic Strategy for Scotland, Scottish Government, November 2010). It also has secondary meanings in terms of minimising impact on the visual amenity of the wider community and enhancing rather than reducing the biodiversity of a site.
To meet this criterion, a hut will ideally exhibit a carbon neutral (or very nearly so) energy strategy. This may vary from no space or water heating all the way through to high levels of insulation and air tightness, combined with only on-site renewables as energy sources.
Using only locally sourced firewood will play a very significant role in ensuring a low carbon strategy for many huts along with small PV and solar water panels in appropriate sites.
The strategy should also extend to the embodied energy and fixed carbon in the materials and construction methods of the hut. A ‘timber first’ materials strategy will go a long way to meeting both of these so long as the timber is sourced and processed reasonably locally.
Reducing concrete and heavy materials will also help because these materials have high embodied energy which means they need high energy to process and transport to site.
OFF GRID (AUTONOMOUS) SERVICES
It is anticipated that many huts will be too remote to make use of mains services. However, where they are nearby, these may be considered if they provide the most sustainable low carbon option with least impact on the immediate site. Many hut builders and designers may prefer to generate their own energy and water supply and to deal with the hut’s own waste autonomously in order to meet more exacting sustainability criteria or specific qualities of service.
For energy supplies, water provision or waste treatment the hut owner must apply high standards of sustainability and there are other regulations that must be followed (for example, SEPA and your local authority maintain wholesome water standards). For more information, see Section 14 on private water supplies, Section 15 on treatment of waste and Section 16 on electricity.
The principles of de-constructibility afford ease of maintenance and recycling opportunities both during and at the end of the lifetime of a building. These principles are described in detail in the SEDA web publication Design and Detailing for Deconstruction:
The publication can be considered as a further aspect of meeting a ‘low impact’ criterion.
Of particular relevance to the timber hut builder will be separation of components to allow individual replacement, for example:the screwing of cladding and decking boards or steel roofing sheets; the bolting of post and beam frames ; the use of galvanized and stainless steel fixings to prevent rusting and difficult removal of fixings.
Where budget permits, higher quality materials will be more worthwhile to recover at the end of the building’s life. Good examples are sheep’s wool insulation (as opposed to mineral wool) and high quality windows and doors that have stood the test of time.
Both the planning policy definition of a hut and the Exception to the Type 23A Exemptions make it clear that the internal floor area of a hut must not exceed 30m2. A raised gallery or platform may increase this area slightly (see Galleries or platforms below).
External access and decking will also add functionality but is subject to planning permission and possibly a warrant if it is above 1.2 metres from ground level (refer to Type 19 Schedule 3 of the Building Standards technical handbooks).
SEPARATION FROM BOUNDARIES AND OTHER BUILDINGS
According to the new regulations set by the Scottish Government, a hut must be at least 6 metres away from any boundary. It must also be separated from any other building (including another hut or associated sanitary facility) by at least 6 metres.
Effectively, where huts are on their own legally defined plots the distance between huts will be a minimum of 12 metres. The reason for this regulation is to help ensure that fire cannot easily spread from one building to another.
WASTEWATER DISPOSAL (MANDATORY)
The term wastewater can refer to ‘black’ or ‘grey’ water. The term ‘black water’ means water which has come in contact with fecal matter (i.e. toilet flushing) and the term ‘grey water’ refers to water which has not come into contact with human solid waste, but may have been used for cooking, bathing, washing or cleaning. You can keep chemical contamination in grey water to a minimum by using ecologically friendly soaps whenever possible.
Any part of any type of wastewater disposal system whether of ‘grey’ or ‘black’ water is subject to a Building Warrant application. On account of this it will be necessary to follow the domestic Scottish Building Standards just as you would for a dwelling. These may be found at Sections 3.7-3.9 in the Domestic Technical Handbook and are dealt with in this Guide at Section 15. Entirely self-contained compost or chemical toilet systems (waterless closets) do not require a building warrant and are described in waste and composting toilets.
GALLERIES OR PLATFORMS (MANDATORY)
According to the new regulations, raised floors, galleries or sleeping platforms may extend up to half the area of the room in which they are located, or 8m2, whichever is the lesser.
This area can be made up of more than one platform but the aggregated area of more than one platform must not exceed the 8m2 limit.
PEDESTRIAN PROTECTIVE BARRIERS (MANDATORY)
The new legislation includes provision for pedestrian protective barriers – in other words, railings, banisters and any type of safety barrier needed to prevent people falling off ledges in your hut.
In order to satisfy the building regulation requirements of Type 23A for pedestrian barriers (ie. to meet standard 4.4), your building and all associated access and decking arrangements should conform to the conditions set out in structural stability and protective barriers.
Wherever there is a difference in levels of 600mm or more, the regulations state that a protective barrier must be provided. This would apply to a sleeping platform internally as much as to an associated stair case, steps, external deck or raised access structure leading to a hut. The barrier may be made of many types of material, but it should present no opening of more than 100mm. Put another way, the barrier should be such that it would prevent the passage of a 100mm diameter sphere.
However, the space between a rise in a stair and the lowest edge of a protective barrier may be larger than 100mm provided the lowest edge of the barrier is not more than 50mm above and parallel to the pitch line of the stair.
The pitch line joins the leading edge of the treads in a stair (i.e. the nosings). In addition measures should be taken to discourage children from climbing the barrier, see Protective barriers to decks, walkways, galleries, ramps and stairs .
The minimum heights of a protective barrier vary according to the following table. The most common situations where regulations would require a barrier will be: exterior decks and walkways which require a barrier height of 1100mm; at the edge of sleeping platforms where the required barrier height is 900mm; and along exterior steps (rising more than 600mm) where the barrier must be 840mm. All these dimensions include a handrail.
In order to meet the dynamic loads (i.e. the varying forces) imposed on a barrier, it should be designed in accordance with Building Standard EN 1991-1-1 and the associated PD 6688-1-1. It is therefore recommended to have the design of any mandatory protective barrier designed by a structural engineer and certified at the same time as the whole building structure.
Any changes in level inside and around a hut, such as stairs and ramps, should offer safe and convenient passage for the people likely to use them.
TABLE OF REQUIRED HEIGHTS OF PROTECTIVE BARRIERS
`Extracted from Building Standard 4.4