What you need to know about Expanded Polystyrene (EPS).

Expanded polystyrene is a method of wall construction that is made up of thick foam membrane built from polystyrene balls. This is similar to the material that is used for packing items in boxes to prevent movement. On its own, the material, with a surface finish pattern similar to that of corrugated iron sheet, is about 75-80mm thick (3 inches). A typical panel is about 1.2 m wide by 3 m high, but upon request, special sizes can be customised. It is to be noted however that slab panels are about 200mm thick.

In construction it is sandwiched between two pieces of welded mesh and a mortar/screed/shortcrete finish applied to either side 20-25mm thick(1 inch). These are sprayed onto the boards to create a sandwich finish which then acts as the wall.

Construction
As a walling material, EPS does not replace any of your typical foundation structure. It comes into play from the ground floor upwards. For bungalows, the process is straightforward as the walls for the house are set out and the wall panels put up while being restrained to the floor. Once all the walls have been put up, they are sprayed with screed and hence become ready for finishing.

For simple Ground + 1 buildings, EPS Can be used as load bearing walls, but they are usually reinforced using angle irons (based on structural design, consult an engineer), which gives the walls sufficient strength to be able to carry a heavier load. In taller buildings, the walls are used in combination with the structural frame where they integrate seamlessly.

Cost
In Kenya, an EPS sheet goes for around Ksh. 7,000 per floor slab and Ksh. 5,000 for the wall slab. Note that this is the cost of the panel from the factory and does not include shipping and installation. These are done at an extra cost. Houses made from EPS average at a cost of Ksh. 35,000 per SQM and upwards as compared to the masonry rate which is about Ksh. 30,0000 per SQM and high quality mabati housing which comes in at Ksh. 15,000 per SQM. It is in the same cost band with high specification precast concrete housing and therefore I would not qualify it as an affordable housing material, despite the narrative that has been strongly pushed by Kenyan Citizens, especially not for a single dwelling unit.

However, it is recognised by the Government of Kenya as one of the affordable housing materials that are locally available and has been used by government agencies to construct a number of affordable homes which are being offered to Kenyans under the Boma Yangu programme.

What are the advantages?
1. It is lightweight and therefore easy to transport and handle, therefore saving on labour.
2. It is fast in construction. It is easily used in areas where projects need to be delivered against a short timeline.
3. It is load bearing for small units such as mansionettes with very light use. (Consult a structural engineer before using this)
4. Insulatory, therefore, has reduced sound transmission from one room to the next.

What are the disadvantages?
1. Vibrations can be transmitted especially where the panels are used as a floor slab.
2. It is more expensive than your typical masonry walling.
3. Polystyrene foam itself is combustible, but it is protected from fire by the screed sandwich.
4. Requires professionals to facilitate proper installation.

Availability
Should you choose to go the EPS way, here are some of the places that offer the materials in Kenya.
1. National Housing Corporation, near Athi River
2. Isopanels Kenya
3. Hong Kong building, on Mombasa road.
4. C-Max on Thika road. This is one of the most reliable sources, located next to the Clay products factory.
5. Koto housing, on Mombasa road, Mlolongo town.
6. EPS 3D, in Ruiru.

Are you looking for other affordable materials to use for your building? Learn more about Kwangu Kwako homes, the most affordable precast buildings in Kenya.