Celotex Wall Timber Framed Cavity Wall Construction Essay

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We have given much consideration to your requirements of delivering an effective and manageable project both in respect of choice of materials and cost of construction and have endeavoured to source the most cost effective and compliant materials, those that will enable your development to meet the current Building Standards and regulations for energy.

We hope the following report meets with your requirements and we look forward to having a good working relationship with yourselves both in the present and in the future.

With regards

G. McWilliams.

Quantity Surveyor

(Design Consultant)

Introduction

For the purpose of this report we have examined the u-values and some different construction methods and materials for the construction of dwelling houses.

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. (Chudley&Greeno,2008)

According to Scottish Building regulations section 6 the following table list the U values for the appropriate elements of any new build home.

 

New Build

Notional U-value

Area Weighted Maximum U-Value

(Backstop)

Wall

0.19

0.25

Roof

0.13

0.18

Floor

0.15

0.20

Air Tightness

7 m3/m2h

10 (Recommended Limit)

Party Wall

0.20

-

 

Improving a building's performance and reducing its impact on the environment is now an essential part of the design and construction process. The envelope of a building can make a significant contribution to reducing the amount of energy it uses through good thermal performance.(Chudley & Greeno,2008)

BUILDING ENVELOPE

Having assessed your typical construction details for each element of the building envelope which are typically made up the following materials:

Walls

Brick

Air gap

Mineral Board

Block work

Plaster board

Roof

Aluminium

Roof insulation board

Ceiling tile

Floor

Carpet

Chipboard

Air gap

Mineral board

Clinker

Earth

We have sourced some alternative construction details and the u-values associated for your consideration.

Firstly we have examined the element of the walls, several construction methods were analysed such as; timber inner frame with a brickwork outer skin; Brickwork outer skin with a blockwork inner skin. Both these methods were investigated with different insulation material and thicknesses used. Generally building with brick and block adds a lot of weight to the foundation. Therefore it increases the stress of the foundation with stronger foundations needed to support the weight. If insulation is specified within the walls this may lead to a wider more costly foundation. The average time taken for the construction process is around 20 weeks for a three-bedroom home (180m2). Site work progresses slower than alternatives such as a timber frame. (National Audit Ofiice,2005)

With all factors taken into consideration, and the u-value of 0.30/m²K required for the element, we have chosen to provide you with details for a timber frame construction and the new u-values associated to our chosen material, inclusive of insulation.

(See appendix A, 1 0f 1 Celotex Timber framed cavity wall)

Timber Framing

The timber frame wall construction method is based on a tried and tested practice that has been in use for over 40 years, this style of build can offer a slightly better U-value against brick and block the United Kingdom Timber Frame Manufacturing Associatioin,2009 (UKTFA) tells us that the massive advantage of timber-frame or kit construction is that it can be wind and water tight within two days by utilising off-site fabrication techniques. This also limits on-site labour costs and limits initial possibilities of water ingress and the reliance of favourable weather conditions throughout critical aspects of the build. This material has the lowest CO² of all building products. Over 70% of home in the developed world are timber frame homes. 60% of Scottish new dwelling are timber frame. In the United Kingdom timber frame accounts for 15% of new homes. Typically buildings were constructed by masonry, this consisted of a 300mm cavity wall with block inner leaf, insulation, cavity and a brick/block outer leaf finished with a plaster render (Chudley&Greeno,2008). Over the last seventeen years timber frame construction has shown steady growth. 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. It provides a faster return on the house builder's investment and greater potential for profits. Some industry experts predict that by 2012 it will account for 50% of the new dwelling market (UKTFA, 2009).

In a recent survey, accredited by the United Kingdom Timber Frame Association(UKTFA), some of UK's leading contractors, developers and architects said they would specify more timber frame in the future. Timber framed construction has proven it is singularly the most sustainable form of construction available in the UK and without question delivers the most thermally efficient, cost effective and safe method of construction(UKTFA,2012)

(See appendix C, Examples of timber framed construction)

Floor

For the element of the floor we have chosen to provide details of a solid concrete floor with insulation under slab. The concrete thickness is a standard 150mm. Although this construction method has been chosen it will be determined by ground conditions. For the purpose of this report we have assumed that ground conditions are acceptable to allow for our chosen construction detail.

According to the Building regulations for Scotland (2009) and the technical handbook for Scotland the desired U -value for a floor is 0.25 W/m²K (Bett,Hoehnke&Robinson,2003).

The U-value for the floor is typically calculated using the P/A method. This involves calculating the perimeter of any building and dividing it by the total of the area as follows;

When it came to calculating the floor area assumptions were made for the type of dwelling house to be constructed. It was decided to use a house type from a similar development from within the locale of Glasgow. With the use of an online calculator the following U-values were calculated.

(See appendix page 1 of 1 Celotex solid ground floor)

Concrete floors with insulation

Concrete floors are built in to increase the thermal mass. Thermal mass is the ability to absorb energy, store it then release the energy when the building cools. Adding thermal mass within the insulated building envelope helps reduce the extremes in temperature experienced inside the home. Insulating the floor also prevents energy being lost to the ground under the floor slab (Emmit&Gore,2006).

Solid concrete floors have good thermal insulation properties. When added with insulation can meet the requirements of the Scottish Building Regulations (2009) by achieving U-values of as low as 0.18 W/m²K. (Concrete Industry,2010). The use of a solid concrete floor slab will greatly depend upon ground and soil conditions of any site. Further investigative work may be required to ascertain the viability of using a certain construction method.

Roof

The next element chosen for the construction project was the roof. The roof is the biggest insulated area of any family home (Emmit&Gore,2010). Thermal loss through the roof is relatively high and typically the roof requires being the best insulated area of any home (Chudley&Greeno,2008). The construction detail chosen for the project was a pitched roof with a ceiling at rafter level. This construction detail is common in most households throughout the United Kingdom.The pitched roof construction is more widely used than the flat roof detail especially in Scotland with the weather being a major factor in any chosen construction design. Again the Celotex U-value calculator was used to determine the U-value for our chosen design. The Scottish regulations calculate that the U-value for a roof should be between 0.20 W/m²K and 0.16W/m²K .For the project in question the insulation is between and below the rafters gave a combined U-value of 0.16W/m²K

(See appendix Page 1 of 1 Celotex, Pitched roof)

Windows

Within the building envelope we have considered for your evaluation the additional element of the windows.

Windows let the light in and allow people to see out but they also interact with their environment. Windows react to outside air temperatures, sunlight, and wind, as well as indoor air temperatures and occupant use, they are strongly affected by solar radiation and the airflow around them (Emmit&Gorse,2010). The lower the U-value, the lower the amount of heat loss, and the better a product is at insulating a building.

The calculated U-values for windows takes into account the airflow around the window and the emissivity of the glass(Emmit&Gorse,2010) Emissivity is the ability of a product to absorb certain types of energy and radiate that energy through itself and out of a room(Chudley&Greeno,2008) A product with high emissivity, such as one pane of clear glass, will transfer over 84 percent of the infrared energy from a warm room outside to the cold air. With all these factors considered, for the purpose of the report and to satisfy building regulations two types of windows have been included for your consideration. The online U -value calculator provided by REHAU was used to process the required information.

(See appendix U-Value calculation REHAU)

Both window types are tripled glazed with a pilkington glass. Thermal transmittance is 1.28 W/m²K.

Part J of the Scottish building regulations demands the installation of energy efficient double or triple glazing with a U-value of 1.8 W/m2K or better.(Bett,Hoehnke&Robinson,2003). With tough zero carbon targets to meet, rising fuel costs and energy efficiency high on the list of priorities building standards predict that eventually all new builds in the UK will be expected to have windows with U-values of less than 1.0 W/m2K.()

Conclusion

When planning any construction project energy loss and sustainability must be considered. The Scottish government has legislation in place to ensure developers meet the required standards and regulations. In addition to the Building Regulations(Scotland), which you must follow, you may be asked to comply with other guidelines including CFSH (Code for Sustainable Homes), SAP (Standard Assessment Procedures), SBEM calculations (Simplified Building Energy Model) and in addition provide an EPC (Energy Performance Certificates) for your desired build.

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