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Реферат на английском языке.
Modern construction comes in many forms, from traditional masonry, to precast concrete, to steel, and in recent times timber frame construction.
Timber frame and masonry construction are very similar looking buildings. Over the last thirty years in Ireland the main type used in domestic dwelling was masonry construction which consists of block inner leaf, cavity, insulation and a block outer leaf, externally finished normally with a brick or plaster rendered block. Over the last twelve years timber frame construction has grown to account for nearly forty percent of the market. Timber frame construction consists of an off site engineered building which arrives to site and the pieces are assembled to complete the unit. The external finish is similarly to masonry with brick or plaster rendered block. The reason for chosen this topic is to find why this change occurred. The purpose of this dissertation is to examine the Irish housing market over the last number of years, also to find out the reasons for timber frame construction becoming more popular.
From a time to construct perspective the length of time it takes to build and finish both forms of construction differs. The construction of a traditional masonry dwelling has a longer time programme than its timber frame counterpart. The main factors contributing to the difference in construction times include.
The programme of works for both methods has a time difference of approximately seven weeks from foundation stage to decorating and moving in stage. Derek Moore of Timberline building contractors states,
"In terms of build speed, timber frame can deliver a significant 30% reduction on traditional construction times, which affect cash flow and reduces local disturbance". (Pick a Pro 2009)
The view of another Irish timber frame supplier is the construction time of both methods of construction is even larger depending on the building,
"Construction time is cut by almost 40% as your timber frame structure is erected on site within days depending on size and complexity of building". (Clark Group 2008)
During the stage whereby the timber frame unit is erected the internal first fixing work can commence. This work can proceed inside the house as the masonry skin is being built, in comparison no internal work can commence on the masonry house while the block work element is being constructed. The long drying out period associated with traditional masonry construction is also a disadvantage in comparison to the timber frame method.
"Apart from the obvious labour saving, timber frame doesn't need any drying-out time, unlike a standard masonry construction, which needs up to 1,500 gallons of water to evaporate before it is dry". (Sunday Tribune 2001)
To reiterate this a leading Irish timber frame supplier states,
"Timber frame aids internal finishes, all walls are straight and plumb, corners are square and true. With timber frame there are less of the "wet" trades, plasterboard needs only to be skimmed and paint, decorative materials and floor coverings can be applied sooner to dried surfaces". (Castle Timber Frame Homes 2009)
For the purpose of this dissertation the author compared the U Value of the external walls of both a timber frame and masonry constructed dwelling, the author also decided to obtain the Building Energy Rating (BER) for both methods of construction so as to make an accurate comparison. Both the U Value calculation and the Building Energy Rating are based on the house plans. With the expertise of Michael Sweeney of Sweeney Energy the U Value and BER calculations were compiled and the results are as follows.
A U-value is the term given to the measure of heat loss through sections of a building. It measures the rate that heat transmits through a component or structure when there is a difference in air temperature at both sides.
"U Values are expressed in Watts per metre Kelvin which is the rate of heat transfer in watts through 1m2 of the structure for one unit of temperature difference between the air on the two sides of the structure". (Roy Chudley 2002)
The following are terms associated with the calculation of the U-Value.
"It is the measure of a materials ability to transmit heat and is expressed as the energy flow in watts per square metre of surface area". (Roy Chudley 2002)
"This is symbolized by the letter R, as representative of a materials thermal resistance achieved by dividing its thickness in metres by its thermal conductivity". (Roy Chudley 2002)
The above calculations show that a traditional masonry external cavity wall has a U-Value of 0.35 W/m2K in comparison to the timber frame outer wall, which has a U-Value of 0.25 W/m2K. The findings for this particular calculation show that the timber frame domestic construction has a better U-Value than its masonry constructed counterpart.
The author decided to compare the Building Energy Rating of both methods of construction. To achieve this the author availed of the expertise of a qualified BAR assessor who calculated both BER values using the same house plans as used for the U Value Calculations. For the purpose of the reader the author explains some of the terms associated in the Building energy rating procedure.
The procedure is based on calculating the energy balance for a dwelling,
"this is the energy required by the dwelling plus any losses, then less the energy gains this is equal to the energy delivered in to the dwelling" (Cheveron Training 2009)
Delivered Energy, expressed as kWh/year. This corresponds to the energy consumption that would normally appear on the energy bills of the dwelling for the assumed standardisation occupancy and end users considered. (Cheveron Training 2009)
Primary Energy, expressed as kWh/year. This includes delivered energy, plus an allowance for energy "overhead" incurred in extracting, processing and transporting a fuel or other energy carrier to the dwelling. For example, in the case of electricity it takes account of generation efficiency at power stations. (Cheveron Training 2009)
The results show that both timber frame and traditional masonry domestic construction have an energy rating of B2 for this house. The B2 rating is acceptable for a building, which incorporates a natural ventilation design.
The primary energy value for the timber frame method of construction is lower than it's masonry counterpart and indicates that the overhead incurred in extracting, processing and transporting of energy to the dwelling is lower for timber frame method.
The comparison of the Co2 emissions results in the timber frame method having lower emissions output and as previously discussed the lower the Co2 emission the better it is for the environment.
Finally the timber frame method had a lower delivered energy rating. This shows that the energy consumption on the energy bills of the dwelling are again lower than its masonry counterpart.
Developers views regarding the change from masonry to timber frame:
To achieve a true indication on the views of the construction industry in regard to both methods of construction and why the trend has moved towards timber frame it was necessary to obtain the views of developers who actually carry out the building works.
As part of the author research, many construction agencies were contacted. Philip Mahoney of timber frame manufactures association was contacted and helped with the author's questions.
Philip Mahoney of the Timber Frame Manufacturing Association said when asked why the trend has moved from masonry to timber frame.
"From a developers point of view speed of construction was very important, because a timber frame house can be up and roofed in a matter of days and ready for the follow on trades to move in. for the developer this was a great advantage as they were in and out much quicker and therefore turn cash over.
Timber frame would have also have got popular with the self build sector because of the fact that a) quite an education process was carried out by the association and its members, b) the green card also began to come into play as well as timber frame is seen as environmentally friendly which the industry has been promoting."
Tom McHugh, Director of Kilcloghans Ltd Galway who have been prominent traditional masonry builders for a number of years said in regards to ease of build "we are masonry builders and we build timber frame, we find that it is especially simple to build the timber frame method" he went on to say in relation to construction costs "timber frame is as economical to build as traditional masonry" regarding construction costs in relation to the downturn in the construction industry he stated "yes the construction cost for both methods had dropped but both methods still work out in and around the same price". He also stated that they found the main advantages of timber frame to be "a drier form of
construction as well as the obvious advantages of speed to build and economical to run". From a selling point of view he found timber frame, "easier for the reason that they are more economical in terms of energy use".
Francis Geraghty Director of Frame to finish building contractors Co Galway stated in terms of ease of construction, "the timber frame method depends largely on the type of house the client wants to build as well as the quality of site preparation before the timber frame building reaches the site". He sees the main advantages of the timber frame method for him are "the U-Values that can be achieved" and also "the whole timber frame structure is up and ready for internal work in a matter of days".
Colm Kilroy a Quantity Surveyor with Michael Higgins and Associates Galway said "from a cost of materials point of view certain materials have dropped in price, but the real drop in price has come from the tradesmen themselves more so for traditional masonry rather than the timber frame method. With such competition for work cost of labour has decreased rapidly". He went on to say, "this drop in labour costs could be a key to the choice of the public in the coming years with traditional masonry getting so cheap to build".
John O' Connell, a builder, based in Co. Galway stated that he sees the main disadvantages of Timber Frame construction as "the inclement weather conditions in this country, have people concerned that timber may rot over time. People also feel more secure with bricks and mortar".
Sean O Donnell a foreman with a building contractor in Co Galway who specialises with both forms of construction sees the main advantages of timber frame over traditional masonry in relation to cost to be "less labour intensive, less wastage of materials on site, and when lived in less cost in running". In relation to time to construct he said, "less time lost due to adverse weather, you get to see the finished product quicker and easier and timber frame leads to quicker installation of electrical wiring". Regarding insulation he states, "with a timber frame house you are closer to the living area and so not heating the outside wall before reaching insulation value, it takes very little to heat up house and the quality of insulation is key to better acoustic performance".
To get a true and realistic view on both methods of domestic construction the author decided to obtain the views of the residents who live in timber frame homes. To achieve this, a questionnaire was compiled and distributed around the Galway area. A copy of the questionnaire is included in the appendix at the end of the dissertation and the results are as follows.
As can be seen from the pie chart emphatically shows that 100% of the surveyed residents notice the timber frame method of construction to be cheaper to heat than its traditional masonry counterpart. The comments received included,
"Traditional block was more expensive; I used solid fuel range with a back boiler and oil central heating. It was necessary to have heat constantly from back boiler toped up by oil, in comparison the oil heating in the timber frame runs for 4 hours per day from November until March to the downstairs radiators only. We have 2 open fires that we never use as it would be too hot. Our oil bill is reduced by 2/3 and we don't require solid fuel".
A further comment stated,
"Timber frame is cheaper as not as cold during the day so no need for much heat during the winter months"
clearly shows that the residents find their timber frame dwellings to be warmer than the traditional masonry counterpart with 84% finding it a lot warmer and 14% of residents stating it to be slightly warmer
shows how well people rate the acoustic performance of their timber frame house in relation to external noises. 55% of the residents find there to be no noise while 45% of the residents find there to be a little noise. One of the residents stated,
"The only noise to be heard is that of the rain water running to the gully".
"External noises are not an issue, but my house is located on a bit of an elevated site and on a very windy day the wind can be an issue".
Other examples of external noises to be heard included traffic from a nearby main road and dogs barking, but no additional noises than would also be heard in a traditional masonry dwelling.