Performance Criteria for Cavity Wall and Pitched Roof

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Performance criteria for cavity wall and pitched roof

Report Contents

Introduction

Cavity Wall

Block

Insulation

Brick

Wall Ties

Plasterboard

Mortar

Elements for a cavity wall

U-Values

Conclusion

Pitched Roof

Types of Roof Coverings:

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There are two basic traditional types of pitched roof:

The benefits of Trussed Rafters:

Conclusion

References

Introduction

This assignment aims to explain the difficulties of performance criteria for an external cavity wall and a pitched roof of a domestic dwelling. This assignment focus on the information provided from the approved document “Conservation of fuel and power in new dwellings” L1A

The main types of walls:

  • Cavity Wall / Cavity walls lose less heat than solid walls, and are much easier to insulate.
  • Solid Wall / constructed from one skin of masonry built from brick/blockwork in this type of walls difficult to achieve high standards of thermal insulation.

Cavity Wall

The cavity wall is the external wall of a house constructed of two parallel walls (two skins), with a space of at least 50mm between them and filled with insulation by many different methods. The outer skin, built from brick or blockwork. The inner skin is usually of blockwork and joins the two walls together by metal tie resistant’s. The weathering is put in at suitable places to prevent the effect of a collapse.

The main function of this external cavity wall is to reduce heat loss by filling the cavity with material that would stop heat transfer; and as such considerably reducing heating costs and condensation. Inside the house cavity wall insulation regulates the heat inside, so it will gives warming in winter and cooling in summer, protecting against damp and mould growth and minimizing sound transfer.

A good cavity wall alone does not prevent the problem of damp; to fully proof a house a good thermal insulator is also recommended. This does nothing for the exterior of the property so there are some suggestions below to help with the endeavour:

Block

The blockwork is made from organic minerals obtained from clay and natural materials, which gives the support and stability for the building. Blocks are built first when starting to build a cavity wall. The benefit of using blocks is that it provides a higher level of thermal mass. When it is well insulated it gives as efficient energy as timber. There are many different types of blocks; block type Thermalite Hi-Strength 7 Blocks with a measurement of 100mm has the U-Value of exactly 0.28 W/m2K for the external wall and has been chosen for those reasons.

Insulation

The decision was made to use mineral wool insulation to fulfil a 75mm cavity wall dimension. This adds excellent performance in relation to heat loss. Mineral wool has high quality glass and relatively light weight. This will mean ease of handling, cutting and installation. Mineral wool insulation is cost efficient which is 50% lower than standard foam insulation. The efficient insulation will be measured for zero heat loss and it can be done by restricting the air movement through the gap between the intern and outer walls. For a zero heat loss achievement the cavity will need to be fully filled. An added benefit to this is the sound reduction properties of the product. The restriction of air through the cavity will also impact on the sound ways trying to permeate the walls.

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Brick

The space between the bricks should be filled with mortar to prevent any leakage or structural difficulties. The excess should then be removed via cleaning to prevent added moisture.

As I have mentioned above, the brickwork is made from organic minerals obtainable from clay and natural materials. This has the versatility of shade, colour and texture. Brick is an amazing material to build with; it provides a pleasing aesthetic to the house with a customizable colour. The raw materials in brick are chemically inserted so it does not contribute to any air pollution in your home. Brick is also fire resistance while being a material that is recyclable and insulating. This allows for money to be saved by lowering heat gain and heat loss. For the use of the bricks a measurement of 103mm brick will be considered for a cavity wall of 75mm dimension. A fully filled cavity wall will reduce the heat loss in the building. The type of brick work selected will be stretcher bond because of the ease of cutting that this material provides.

Wall Ties

Ties when correctly fitted should slope downward from inner to outer wall. This helps to prevent rain and other weather related matter to cross the cavity. This will add another aspect of moisture protection for the inside of the house.

For the 75mm cavity wall; 200mm wall ties were selected to be places between the blocks and the bricks. The horizontal joints will also be attached to wall ties, to give the wall more stability. This will prevent the likelihood of drift between the walls. The material will also be made from stainless steel so as to prevent corrosion of the metal.

Plasterboard

Lightweight Plaster (Inner Finish)

Mortar

The decision was made to include a thin layer of mortar to the brick/block work. This will:

  • The build time will be reduced because of the ease they are constructed. Construction time can be less than 60 minutes until the material is considered dry and ready for component installation.
  • The material increases the thermal performance of the building and in so doing will reduce the U-Values.
  • The thin Mortar will improve construction quality

Elements for a cavity wall

The following materials were chosen for the creation of a suitable cavity wall:

103mm brick Stretcher bond

75mm cavity wall fully-filled with insulation

100mm block Thermalite Hi-Strength 7

200mm wall ties

Thin Mortar layer

Lightweight Plaster for inner finishing

U-Values

The projected heat loss will be calculated depending on the U-Values. The lower the value the better the material as is shown in L1A documentation. This document provides that if the U-Value is less than 0.2 W/m2K then evidence is needed to confirm that the building design is viable.

Conclusion

External walls are considered to be thermal element. That being considered the main purpose of insulation is to conserve fuel and power in new dwelling. It prevents the penetration of weather to the internal surface of the wall. The added benefit of reducing the owners carbon footprint by improving the energy-efficiency of the home means that this is of great importance. This creates the advantage of dramatically reducing the amount of heat needed for the living space.

This means that unless heat is already generated by a heat pump the likelihood is that the home will require gas, oil, coal or gas to produce heat. These all have their impact on the environment so reduction of use is needed.

The external wall is not just for the inter benefit as a good external wall can add great beauty to the appearance of the building.

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Pitched Roof

Pitched roof is a type of the ceilings which consists of two surfaces slotted together from the end top of the walls to converge together in the top such as a corner (collectively called roof) required by the nature of the design and the type of construction. The use of such roofs is popular in areas of high rates of rain or snow and the main purpose of a pitched roof is to protect the house from the wind (weather resistance), rain and redirect water and snow as much as possible to conserve heat inside the house.

Types of Roof Coverings:

  • Asphalt Shingles, the asphalt shingles still standard because they are economical, used on most roofs in many colours, and may last for long time.
  • Metal, such as Steel, aluminium and copper characterized solidity and low maintenance.
  • Wood Shingles and Shakes, as friend of environment and is a popular choice for homes
  • Concrete or Plain Tiles, tile is easier to use than concrete and roofing tiles are fire-resistant and easy to fix it
  • Slate, it is very expensive but beautiful and resists fire and mildew.

There are two basic traditional types of pitched roof:

  • Purlin pitched roof (cut roof) / Cut roof timbers are made on site and building up the roof using rafters, ridge boards, joists and purlins where they are fixed in the location
  • Rafter pitched roof (truss roof) / they are designed in the factory then delivered to place ready and complete and just erected. Moreover each type could be warm deck or cold deck.

Trussed Rafters this type of roof is mostly used for housing and is currently designed by specialists in the industrial companies by using computer design. After the completion of the design, the roof is moved to the site and easily installed in the specified place.

Trussed Rafters are fast and easy to sit and moreover can be designed so adding more rooms in the roof is possible, called attic trusses. So the recommendation would be to use Attic Truss (room in the roof) type of trussed rafters because it is quick and easy to sit on site, collecting in the factory as a fit quality for Attic trusses, specially designed to carry all excess weight.

Roof truss photos

The benefits of Trussed Rafters:

  • Suitable for many types of the roof structures
  • Fast construction and on time delivery which is cheaper than other due to the ready components
  • Easier fixing so not as much work
  • Simple industry process’ reduce the emissions and pollution
  • Thermal insulator is better than others and more flexible than many other methods of roof construction

Conclusion

The Pitched Roof is a very important section of the house so it must be built well, strong, stable and durable. This means that the house will be protected from the outer climate factors such as the sun, the air, the rain and snow. This also will mean that the the spread of fire from house to house is reduced as the insulation will keep the heat inside the house. This will support warmth as much as possible because it is the main area from the house where heat loss may happen. Pitched Roofs are able to support loads (weights), the slope of the roof has a main effect on the aesthetics and the right colour is selected it will give the home a beautiful shape.

E:\finish\AtticTruss.png

References

L1A Conservation of fuel and power in new dwellings

http://australbricks.com/sustainability/the-benefits-of-bricks/

http://source4me.co.uk/calculate_cavity_wall.php

http://www.glengery.com/brick-products?utm_source=glengerybrick.com&utm_medium=domain-referral&utm_campaign=301-redirect

http://australbricks.com/getmedia/256750aa-5b5d-4e15-94e2-9cf896a23b73/Bricks-For-Living-Brochure.aspx/

http://www.markgroup.co.uk/homeowners/insulation/cavity-wall-insulation?gclid=CPKMrd7A-cECFRMatAod0DsAjA

http://www.planningportal.gov.uk/permission/commonprojects/externalwalls/

http://www.unitedinsulations.co.uk/cavity-wall-insulation-faq

http://www.homeworksenergy.co.uk/external-wall-insulation/

http://www.greenhus.co.uk/about-external-wall-insulation/benefits-of-external-wall-insulation/

http://www.ask-hanson.com/u-value-calculator.html

http://www.diydata.com/general_building/roof_construction/roof_construction.php

http://www.planningportal.gov.uk/permission/commonprojects/roof/

http://www.builditgreen.co.uk/products-services/roof-finishes.html

http://www.tra.org.uk/trussed-rafters.php?id=30

http://www.fforest.co.uk/PDFs/wolf_systems_trussed_rafter_technical_manual.pdf

http://www.trada.co.uk/images/onlinebooks/7E93B0B4-0131-475E-8C39-563AD4FBF9E9/

http://great-home.co.uk/a-guide-to-roof-construction/

http://www.kingspaninsulation.co.uk/Services/Technical-Services-Department/U-value-Calculations.aspx

Mike, R; Alison, C (2014).Construction Technology 1: House Construction. 3rd ed. Hampshire: PALGRAVE MACMILLAN. 276-294.

Numan Samha 1420688