Knowledge

The condensation point in the wall is where the hot, warm, moist air (approx. 21°) inside the house meets the cold outside air (approx. 5°). Rule of thumb: The condensation point, should be in the middle of the insulation. The dew point can only be accurately calculated when all the insulation is fitted together. It is always important to have a wall construction that is breathable and allow moisture to pass through it. You should go from a low level of breathability on the inside to higher level on the outside hence moisture is moving outwards all the time.

With the new building regulations and the move towards better U-values in the walls (for example, 0.27 in 2008 to 0.17 in 2013 [the lower the number the better the U-value]) there are positive and negative effects. The positive effect is the house will be warm and less heat will pass through the walls meaning lower heating costs. The negative effect is that there are higher moisture levels inside the house that can lead to poor air quality when not dealt with in an appropriate manner. One of the best ways is to deal with this negative effect is to ensure that your wall construction allows this moisture to pass through the building envelope and to evaporate outside. This is what is knows as breathable wall construction.

Part L of the building regulation looks at reducing the wall vents in homes. This will lead to the move towards controlled mechanical ventilation known as HRV. However there are positive and negative consequences of this. The positive is that you reduce the drafts in the house, which reduces the amount of heat leaving the building. The negative effect is when you remove your vents you increase the possibility of condensation forming inside the house. This is a common problem when you have north facing walls or poor windows.

When you start looking at low levels of U-values in the windows, like your walls, you have to consider the condensation (dew point) where hot and cold meets. In most passive windows there is a 5mm ventilation space between the outside clad and the inside frame, better known as a thermal break.

As Ireland embraces building low energy homes, there is a shift to using more modern and intelligent materials. The traditional felt that was used on homes was not breathable and did not allow for moisture to pass through. As a result new breathable felt has been developed to allow moisture movement through the felt whilst allowing for rain protection from the outside.

When constructing a dormer or a warm pitched roof, you are required to fit the insulation up tight to the breathable membrane. It is recommended to double batten the roof on the outside. This allows for good air movement over the roof.

Thermal bridge is where you have an outside surface making contact with an inside surface of a house. With more modern complex buildings, for example dormer windows and corner windows, structural details need to be looked at for thermal bridging. Also when cavity closures are used with block build houses and at foundation level.

The blower door test is a machine with a fan that checks the building envelope for air leaks and draughts. It does this by pulling air into the building and pressuring the building to 50 Pascal’s, like blowing a balloon up, if there are any holes in the building envelope they will be quickly identified using a smoke machine. The same test is repeated in reverse to ensure that you have good window seals. This test is done with all vents and chimneys closed and the result is given based on this. If the chimney or open fire is allowed to remain open it will act like a vacuum pulling heat outwards. The more airtight the building is the more heat will be pulled up the chimney. In order for the HRV to work effectively your airtight test should be 1.5 air changes per hours or lower, 0.67 being passive.

No it is not.

When you have a low energy house it is vital to have total control over your heating. It is not good enough to say you have 3 heating currents 1) upstairs, 2) downstairs, and 3) hot water. The house needs to be divided into room heating circuits and controlled separately by its own wall stat, on the wall that, will turn off that circuit when the required temperature is reached. This is important as if you have passive solar gain through the window during the day the temperature in that room may have been already reached thus no need for heating.

In 2015 the European norm for all new construction will be low energy/passive standard construction. The U-values in walls, roofs, and floor will be as low as a 0.12 U-value and renewables will provide for most of the space and hot water needs of the house. This makes very good sense, as we cannot stay constructing houses that have big heat demands and high environmental impact.

A HRV must be designed to provide fresh clean air into the building and to remove stale air from the building. In this process when the stale moist air is being extract from bathroom, kitchen, utility areas it preheats the fresh air coming from outside (5-19 degrees). The two airs don’t mix but passes through a unit knows as a heat exchanger. The HRV unit is not a humidifier and should not be confused for one, as it the humidity in the air that gives it better heat transfer through the heat exchanger. If we were to take the humidity (moisture) out of the air you would start to feel it in the back of your throat.

Yes, the solid fuel appliance should have an external air. When you have a HRV the air changes per hour is normally 1.5 times. When lighting, a solid fuel appliances requires on average 40 cubic meters of oxygen or air per hour hence it is very important that the appliance has an external air connection from outside for the combustion.