Rammed earth with turf roof specification
From Sustainable Building Resource
At RDE we did a short project with a WSA student who produced a series of examples on how to extend properties and one of these was to look at how to extend your house (brick construction) using a rammed earth and green roof option. We hope that the info below is useful, even if it is just guidance.
Construction Overview
The main construction sequence to think about when constructing rammed earth is the use of formwork. This is the temporary support used in the soil compaction and can be removed almost immediately after compaction. There are two main different types of formwork static, which uses reinforced concrete formwork or moving formwork, which requires a setting up at each fill. There are then further styles for each. The face of the formwork plays an important role in the finished face of the wall. Care should be taken with a very smooth formwork so that material is not plucked off and should be slid across the surface to break the seal between the two faces. Appearance of the wall will lighten in appearance over time. Corners and other fragile edges should be chamfered or require protection. Slenderness should be limited to twelve for load bearing walls.
It is important to remember that the construction details shown here are only a given example and that it is the constructions principles, which carry rather than the chosen detail and plan. In the construction example shown roof joists have been exposed for aesthetic preference and position of openings for ease of presentation purposes. Earth walls are typically 300 – 450mm thick. Walls can be insulated internally or externally. The presence of movement joints is essential as in any solid wall construction. Every situation will vary. Professional services are always a wise choice.
Construction Details
A. Foundation and footings
Provide a continuous damp proof material between the footing or plinth and the base of the rammed earth wall
Heavy duty plastics-based damp-proof coursing are commonly used to withstand ramming without damage
For exact foundation type and size a professional engineer should be consulted
B. Windows and Openings
In the example shown the window opening continues all the way to the eves, this allowing a simpler detailing and building sequence when ramming. If lintels are used within the rammed earth structure they should be at least 300mm for spans up to two metres and general practice followed for weak masonry
Allowance for dry shrinkage should be made for incorporation of window cills.
For spans up to 1m box shuttering inserted within the formwork will be the most effective means of providing openings.
Forming can be used using temporary block outs or incorporating supporting lintels during construction. The simplest is to extend the opening to the height of the full wall.
The combined horizontal length of the openings in wall should not exceed one third of the total length of wall.
Minimum distance between openings should be at least 600mm
Openings should be at least 750mm from the internal edge of a wall corner
If openings are formed by arches there must be at least 450mm material above the crown
C. Eaves and Roof
Make sure insulation detailing is continuous Around the eaves
It is common practice to provide a wall plate or ring beam continuously along the top of the walls for structural stability. They are normally either timber or reinforced concrete. The timber detail shown uses anchorage bolts or ties fixed every 500mm.
D.Existing and Proposed floor junction
Where heated floor has been used fibreboard insulation between proposed floor and existing foundations deters heat loss
E.Roof Junction
Standard flashing and medium board upstand to protect existing wall
F.Proposed opening and existing wall junction
Where the existing wall is weak, providing a full height opening between the proposed and existing construction offsets potential damage from ramming. In this particular example a door opening and frame has been constructed.
G. Proposed and existing wall junction
Where both walls meet it is important to allow for the variation of movement, horizontally and vertically. The wall tie shown especially allows for this vertical slippage.
Some old buildings can move a lot seasonally.
It is recommend that you get an engineers input as a good long term investment
