GENERAL #

This Section will help you and your engineer decide what type of foundation is appropriate to your site and superstructure design. Types of hut explains what types of hut this Guide deals with and what types it does not cover. 

Accordingly the four foundation types detailed in this Section are specifically intended for the two models detailed in this Guide or other relatively light weight, timber-framed constructions (without masonry or turf roofs) which may be designed in collaboration with a structural engineer.

PURPOSE OF FOUNDATIONS #

The purpose of foundations is twofold: firstly to spread the weight of the building and transfer it to the ground in such a way that the ground can resist the load without subsidence; secondly to tie the building down against wind uplift and overturning. 

Foundations must be robust enough to survive in the site conditions found, which may include relatively mobile sands and gravels, soft peat, running water, flooding and frost heave. They should be capable of being installed without major machinery or vehicular access. Preferably they should be removable at the end of the building’s life to meet the planning definition of huts (see Planning permission). 

TYPES OF FOUNDATIOINS #

Four examples follow that are suitable for the engineered model hut designs and for variations of these models which you may design with professional assistance. This section describes important aspects of each type that will help you decide which type is most suitable for your site conditions, hut design and available resources.

FOUNDATION DETAIL – PADS #

One pad is required for each post in a post and beam building and this method is particularly suitable for sloping sites allowing different posts to be different heights according to position on slope.

Where bedrock is present the concrete will be taken down to sound rock and may be pinned to the rock with steel dowels. Pads can also be spanned by large timber ground beams that can then support stud-framed structures. 

FOUNDATION DETAIL – STRIP FOUND #

This method is suitable for stud wall superstructure and relatively flat sites. This found comprises low poured and shuttered concrete walls on concrete trench fill. Clean to the bedrock where near surface and use trench fill to make a level base for the wall form work (shuttering).

 The principle can be applied using blocks or bricks to form the wall and limecrete to provide a more ecological strip found, but these alternatives have not been assessed by our structural engineer and need to be researched by the hutter

FOUNDATION DETAIL – POLE #

This method is suitable for stud framed superstructure and can accommodate sloping sites with different heights of pole. Poles can be treated telegraph poles (including recycled) or precast concrete piles, augured or dug. In true pole framing, the poles would extend up and form the superstructure of the building.

The design could also be adopted for a post and beam superstructure where the pole can be accurately placed and the connection detail between post and pole is robust.

FOUNDATION DETAIL – PRE-CAST SLAB #

Using readily available, standard pre-cast concrete slabs, this type is suitable for stud framed huts on relatively flat sites.

THE SPACING OF FOUNDATIONS #

The foundation plan will depend on the design of the superstructure. A strip wall foundation such as that shown in figure 4B will have two or three runs maximum 3.0 metres apart with the hut floor beams spanning between. 

A pad foundation such as 4A will be located at the bottom of each of the posts in a post and beam superstructure. The Precast Slab 4C and Pole 4D foundations are also taking a point load like 4A but are designed to support a ground beam substructure to the hut onto which a timber frame is erected. They should be in a grid with a maximum spacing described in the Appendix to this Guide. (see Appendices for beam and floor joist sizing).

TIE DOWNS – SONNECTING FOUNDATIONS TO SUPERSTRUCTURE #

The Post and Beam hut is bolted down to its pad foundation as shown in figure 4A. The Stud Frame hut will have one of the following options: a platform floor nailed to the wall plate as figure 4B; or with twisted ties connecting its ground beams to the foundation as shown in figure 4C; or twisted ties connected to the ground beams already bolted to the foundation in the case of figure 4D.

THE USE OF TIMBER IN FOUNDATIONS AND SUPERSTRUCTURE #

Foundations will be surmounted by a wall plate or ground beam. These must be durable or moderately durable (see Durability of Timber). This is achieved by using treated softwood timber or a naturally durable timber such as the heartwood of oak or larch. The timber is normally kept out of the ground and protected from rising damp by a damp proof course (dpc). Separation from the ground by at least 150 mm is considered necessary to avoid rain splash whilst the hut above will protect the foundation timbers from driving rain.

Generous roof overhangs, well designed rainwater gear and wider claddings all help to keep foundation timbers dry. Exceptions include type 4C where oak blocks are protected below the building and type 4D where the durability of the pole is achieved by treatment.

SOLUM #

It is not necessary to treat the solum under a hut but it may be considered desirable to remove ground vegetation, lay a membrane and cover it with stones before the hut is constructed. 

If animals are to be excluded from underneath the building this can be achieved by putting up a mesh screen. Any such fence or screen should be well perforated to allow a free flow of air. This is necessary to ventilate the underside of the floor and so prevent condensation.