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Building Contractors

029-56311

info@mgroup.ie

021-4975979  info@mmd.ie

Passive & Energy Efficient Builders

                 Phone:  022-27494

info@magner.ie        

 

BUILDING STRUCTURE AND FABRIC.

Renewable technologies have become a major factor in the building industry since the early 2000s. However a greater deal of emphasis on these technologies especially in domestic dwellings has arisen over the last 5 years or so. This in turn has also increased the importance of insulation standards, cold bridging and airtightness throughout a building’s fabric in an effort to minimise heat loss. Reducing heat loss will reduce your heating needs and thus reduce your energy consumption and costs. One of the great advantages of building a new dwelling is that it gives you the chance to incorporate and even enhance the latest regulations that have been created to improve the comfort quality while utilizing the full benefits of the renewable technologies now available. 

Insulation.
The general synopsis for insulation in new builds is much the same as that for an existing dwelling, which is dealt with under the “Insulation” tab to the right. New houses must at least comply with Part L of the Building Regulations 2007.


Element Area

U-value

Pitched roof with flat ceiling

0.16

Pitched roof with sloped ceiling

0.20

Flat Roofs

0.22

Walls

0.27

Ground Floors

0.25

In new dwellings however, there is now a huge focus on reducing or even eliminating “cold bridging”. This is the term given to areas where a warm internal solid area meets a solid cold external area with no break for an adequate layer of insulation. These areas occur due mainly to either structures bridging the inner leaf with the external leaf of the external walls or poor detailing with insulation in critical areas. The main areas of concern are normally where floors and ceilings meet external walls and also around openings in the external walls for windows and doors.
The importance of trying to eliminate “cold bridging” in your new dwelling cannot be emphasised enough. This can be achieved with good details on the insulation placement in the critical areas. Also care and thought should be taken in the design and construction of the building’s structures. You would be strongly advised to consult professionals for advice on this, even if you are building with standard techniques and products i.e. cavity filled walls or timber frame. It should be noted that cold bridging can cause in excess of 20% of heat loss, in an otherwise well insulated building.

Airtightness.
The airtightness of a building can be a fundamental component in the amount of heat loss from that building. The single biggest heat loss point of a dwelling can be its chimney. Other critical areas are suspended floors, flues, pipes, attic hatches and around windows and doors. This leads to unwanted airflow and air leakage. Some solutions are as simple as blocking the chimney with a “Chimney Balloon” when not in use. Others relate to good detailing and supervision during the construction of the dwelling. The two main options to create an air type barrier are with a wet mix plaster coat (masonry inner leaf) or with an airtightness membrane and tapes. It should be noted that using either of these techniques will only be as effective as the attention paid to the detailing and fitting/applying of same. Professional advice in this area is undoubtedly required prior to construction.
As important as airtightness is, a house should never be sealed up completely, as a minimum of fresh air is required for health and safety reasons, therefore it has to be balanced with ventilation. 

Ventilation.
Adequate ventilation is essential to provide fresh air and to remove moisture, odours and pollutants from the room air.  However, excessive ventilation can result in energy wastage and create draughts. The building regulations require the following as a minimum:

All rooms (except bathrooms and WCs) must have a controllable background vent of 6500mm.sq. (100 diameter wall vent or 15mm X 435mm window trickle vent), and rapid ventilation of 1/20 the floor area (openable section of window or door).

In addition to the above all kitchens and utilities must also have either a mechanically vent or a passive stack vent (PSV).

Bathrooms must have rapid ventilation of 1/20 the floor area and a mechanically vent or a passive stack vent (background wall vent not required).

WCs (small toilets) must have rapid ventilation of 1/20 the floor area or mechanically vent or a passive stack vent (background wall vent not required).

If an open fire or other fuel-burning fireplace appliances are to be installed, they should have an independent air supply.  This can be achieved by means of an under floor inlet or by using a room sealed appliance such as a balance flue.

These regulations are minimums for standard construction and may require higher values in complete airtight building design such as passive buildings etc.
There are other ventilation systems that can achieve the regulation requirements and yet have less interference on the air barrier of your dwelling. These include complete Mechanical Ventilation Systems (which can also have Heat Recovery) and Smart Vents (which only open when necessary via humidity sensitivity controls). Attention should be given, irrespective of which system you install, to ensure that the building remains well sealed.  Services should be designed with minimum penetration of pipework and cabling through the building’s air barrier and insulated shell.  Doors and windows should come with factory-applied draught seals.  Porches and draught lobbies can also reduce draughts at external doors.

 

   
 
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