Abstract

This report intends through a case study to investigate if lightweight concrete is

appropriate as main material in the outer wall of a seven storey residential building.

A technical design is carried out in accordance with the definitions and requirements

for passive houses, given by FEBY’s1 “Demand specification for passive houses”.

A literature review is also carried out for a comparison between regular bolt wall and

light weight concrete wall, with a focus on the safety of moisture.

The lightweight concrete block used in the report is as a celblock produced by the

company H+H Sweden AB.

The methods used have resulted in compliance with requirements and

recommendations from authorities. Calculations of energy, noise and moisture risk

assessment has been carried out.

The work has resulted in the conclusion that the lightweight concrete itself is not

able to isolate in the extent necessary to obtain chosen U-value of 0,1 W/m2 ° C,

without getting to thick. Therefore additional insulation is needed. There are few

relevant reference objects built with only light weight concrete. A villa in Lomma,

Sweden, has been designed but is not yet built. The house has no additional

insulation and the climate screen consists only of light weight concrete and plaster.

The multi storey building designed within this report has generally large windows,

also to the north, which in passive house context is unusual. The large window areas

result in greater thermal bridges around the windows and greater losses of heat

through transmission.

As compensation a very low U- value of 0,1 W/m2 ° C was set as a prerequisite from

the start ensuring a positive energy balance. This action has proved necessary when

implemented energy balance calculation resulted in the heating demand of 42

kWh/m2 per year. Maximum allowable energy for a passive house is according to

FEBY under 50 kWh/m2 per year.

There are several advantages identified when using light weight concrete. All

problems related to moister are avoided with this completely mineral material. Light

weight concrete offers good thermal insulation by its porosity. It has heat storing

properties during the winters. The material is fireproof and free from chemicals.

Together with additional insulation a quiet and healthy indoor environment is

derived.

It has been difficult to find potential risks of using concrete in the climate screen of

a passive house. Passive house technology is relatively new, and passive house

technology with concrete is even newer. In fact, the villa in Lomma is said to be the

first in Sweden carried out in light weight concrete. A minor estimation upon the

costs of a the insulated light weight concrete wall, contra a wood bolt wall has proved

the light weight concrete wall to be twice as expensive. Perhaps the future will prove

risks that have not yet been revealed?