Ekobyn Mjölnartorpet is in the eastern part of Kronoparken in Karlstad and consists of 18 single-family houses. The houses were built in 1995 and after almost 30 years, a question has arisen about how the houses' energy use and ventilation have been affected. When one of the houses was renovated, the residents could see how the loose wool insulation in their outer wall had collapsed and did not cover the entire surface of the wall. This caused the condominium association to ask itself the question if this was something that could be widespread throughout Ekobyn. Furthermore, the association asked itself the question of whether the ventilation system had changed during the same time, and how good the air flow in the houses is. The houses today have a self-drafting system with a kitchen fan supplemented by an exhaust fan. In this work, a house in Ekobyn has been investigated and evaluated regarding the house's insulation and ventilation.The challenge in the report was to make estimates with limited data and take account of uncertainties in calculations and measurements. The approach was to circle values in a range to be able to show that somewhere in between lies the real value. The work has been divided into two parts.In the study on insulation, it was found that after an investigation with a thermal camera there was a widespread problem with collapsed insulation in most houses. The residents experienced comfort problems on the upper floor and most of the insulation holes were where there were missing windows and doors on the wall as well as in corners and at the slanted ceiling on the upper floor. With two different approaches, a calculation model was designed and the size of the transmission losses from a square meter of outer wall could be calculated. With the help of the present value method, a maximum price for a measure per square meter could be produced. A measure would have to cost a maximum of SEK 409/m2 in one case, but in the most favorable case be profitable if the cost was SEK 1,320/m2. From a comfort perspective, it is not worth doing the measure to get a better indoor climate on the upper floor because it will not affect the transmission losses right there. In terms of energy, it is beneficial to do this because energy use will decrease, which is also positive from an environmental perspective.In the study on the house's ventilation, it was found that both fans worked, and the air flows were examined when the fans were partly switched off, partly when they were running at max. The air flow in the house was substandard on both measurement occasions, which took place at 0°C and 15°C. To investigate how the air flow varied under different outdoor temperatures, a calculation model was designed. It calculated the air flow through each air device for different outdoor temperatures. The result showed that there was substandard ventilation and thatthey almost never met Boverket´s requirements for indoor ventilation. Therefore, today it is recommended to run the fan at maximum all the time, but turn it off when the house is empty and below -12°C. The fan should be replaced in the future and, according to the results, it should be able to deliver at least a drive pressure of 27 Pa.In the discussion, various uncertainties are raised and what effect they may have on the result, for example the value of the house's total heat loss factor. When it increased by 20%, the savings per year increased by 16% in the most profitable case and 10% in the other case. Both for the insulation part and the ventilation part in the report, the results were presented in different types of intervals, to take the uncertainties into consideration.