Natural Light & The Heat Loss Fight

 

  The greatest potential for heat loss is through glazed windows and doors, fortunately modern triple glazed units  can now achieve a  transmittance or ‘U’ value as low as 0.7 W/m2K which is far more effective than a traditional single glazed unit with a ‘U’ value of around 4.5 W/m2K. Both triple and double glazed units of the highest rating will be utilized in the new house. 

Double glazed windows will be used in the south facing elevation as the area of glazing is nearly half that of the north elevation, this will take advantage of the extra sunlight a south facing window receives and will help to balance the overall solar gain. The larger north facing glazed units afford the best view from the property but will also suffer the most from wind chill, because of this, all windows and doors facing north will be triple glazed. Both the double and triple glazed units will be Argon filled and manufactured with low emissivity glazing. The glass within low 'E' glazed units has special reflective coatings which reflect heat back into the room, the coating has very little impact on the transparency of the window unless tinted by design, a very slight tint may be visible from outside under certain conditions.    

MVHR. Mechanical Ventilation & Heat Recovery

 

At the heart of the MVHR system is a compact air handling unit that has a highly efficient heat exchanger within, the unit draws fresh air from outside which is heated by the thermal energy taken from the used air it extracts. When designed and installed correctly MVHR units are very quiet and should achieve a heat recovery of up to 95%. The efficient heat recovery of an MVHR system means that there is very little compromise of the buildings thermal envelope. While such systems do require energy to run, the amount of energy saved far outweighs what would otherwise be lost through a poorly insulated, ‘leaky’ construction.

Above & Below shows the flexible ducting for the MVHR installed between the floor joists.

The roof is battened ready for tiling as the first layer of render is applied to the exterior.

Ducting for the MVHR system is installed along with the other main services.

The layers of PIR insulation are fitted between the roof trusses and made air tight.

First floor decking is laid.

The first layer of external render is finished and tiling to the roof continues.

The lattice of the posi-joists allow for easy installation of service pipework and ducting.

The first floor studwork partitioning is erected.

The MVHR ducting is insulated before the voids are filled with mineral wool.

The second layer of external render has been applied and the roofing tiling is complete.

Painting of the external render begins.

Clearing The Air

Through design and construction we have ensured that our building has plenty of highly efficient insulation in order to greatly reduce the amount of heat lost through the fabric of the    building, however, the effectiveness of our ‘thermal envelope’, also relies on the building being airtight, therefore steps are taken to seal any areas where air leakage may occur, some of which are highlighted below.

Above:Polyurethane expanding  foam has been applied to seal around posi-joists at each end. 

 Below: Sealant has been applied around insulation at window and door reveals, and to full depth

               around each frame. The excess foam will later be trimmed flush before  rendering.

Of course an air tight building will very quickly become a ‘sick’ building unless adequate air circulation and ventilation is provided. We can immediately see conflicting requirements, on one hand we have the need to prevent heat from escaping, and on the other a building and occupants that we must keep healthy by preventing the build up of moisture and stale air. In short, we need to keep the heat in, the moisture out and provide fresh air for everyone inside to breathe. In order to achieve all the above requirements and tick this seemingly contradictory set of boxes, our clients new home will have an MVHR system designed and installed. MVHR stands for  Mechanical Ventilation and Heat Recovery, this will allow the building to be properly ventilated with very little loss of heat.

The first roof trusses arrive on site.

The roof trusses are craned into position.

The diminishing truss set is put in place.

The roof trusses are braced and tied as the gable walls are completed.

The main structure is ready for rendering and the roof ready to be covered and tiled.

Internal Insulation

We do not only insulate the exposed areas of the building, we also use insulation within the internal floors and partitions. Here we have specified 200mm thick mineral wool between the floor joists and also 100mm mineral wool between the members of any stud partions. Insulating what would otherwise be structural voids in this way, not only reduces the risk of fire spread, but also offers better sound insulation between rooms and floors.

  Good insulation between rooms and floors also increases the potential to save energy by providing greater control over the dispersal of heat throughout the building. This means that energy is not wasted trying to keep the temperature in one room higher while heat otherwise escapes through the walls and floors into another.

Roof Insulation

  There are several different methods we could use to insulate the house at roof level. Here  the trussed rafters are 200mm deep which accommodate 175mm of PIR board insulation, laid in two layers. The insulation is installed between each rafter and flush with the lower edge of the rafters. A 25mm air gap has been maintained above. Rafter level insulation is typically used in ‘warm’ roof construction. A degree of thermal or cold bridging occurs through the rafters because the heat conductivity of any timber is much higher than PIR board  meaning that heat will be transmitted through 200mm thick timber much more quickly than through PIR board of equal thickness. Potential cold bridging can be reduced by having a third continuous layer of insulating material either below or above the rafters. Any joints between the PIR boards are taped as within the cavity wall.

   Insulation within the rafters is only continued up to ceiling height. Above and between the ceiling ties 300mm of mineral wool insulation will be laid, again in multiple layers, with the thickest being applied as a continuous layer over the top. Although mineral wool is not as effective as PIR board, it still offers high level of insulation at this thickness. Where the two types of insulation meet it is important to try and eliminate any gaps, either with staggered taped joints or by further packing of mineral wool.

   Any remaining attic voids above the insulation are classed as ‘cold’ roof areas and are ventilated to eliminate risk of condensation. In this case ample ventilation is afforded via special tiles that are installed in the roof to maintain access for bats into a protected bat loft.

The inner structure reaches the ground floor ceiling height.

The first floor joists can now be fixed in place.

With the first floor underway, work on the cavity walls continues.

 

Cavity Wall Insulation

Because we are using a traditional cavity wall construction and not something like SIPs (Sandwiched Insulated Panels), we have used an extra wide cavity, this is in order to accommodate a more effective thickness of insulation. With a cavity width of 200mm we are able to install 150mm of PIR insulation, retaining a 50mm air gap. The effectiveness of any rigid insulation is reduced at joints, so two 75mm layers have been used rather than a single layer. Using two layers allows us to stagger the vertical joints where each PIR board abuts with another within the cavity.  All remaining exposed joints are then taped, this also greatly  minimizes any air leakage.

We have


calculated that this cavity wall specification will achieve a ‘U’ value much lower than required by legislation, being almost twice as effective at reducing heat loss. PIR board insulation can also be used to line walls internaly or externaly. This may be used as a solution for insulating solid walls or timber frame structures.

A 200mm cavity requires the use of extra long wall ties which tie the inner and outer block skins together. Various types of extra long wall tie are now available. Here we are using basalt fibre based ties, which have very low thermal conductivity, this further reduces potential cold bridging.

Ground Floor Insulation

To insulate the ground floor we have used 150mm thick Polyisocyanurate insulation, this reduces heat loss through the floor by almost double the mandatory target. Polyisocyanurate or (PIR) insulation has an almost unmatched level of thermal resistance and today is commonly specified in a wide variety of applications. Although ‘man made’, much of the raw component is recycled content, PIR board has zero ozone depletion potential and virtualy no global warming potential.

Highlighted in the detail above and shown in the photograph is a load bearing insulating element which is laid at low level as part of the cavity wall inner skin, this is used to prevent  ‘cold bridging’, essentialy this  greatly reduces potential heat loss through the internal blockwork to maintain a very low overall ‘U’ value. The ‘U’ value is the rate of thermal transmittance and when calculated takes into account the gauge or thickness of  the material. The load bearing insulating element we have used is similar to PIR board but with a much higher compressive strength.

Anatomy of Thermal Efficiency

 

In order to maintain a very low level of heat loss we form a near unbroken barrier or envelope of  insulation around the building. Insulation is laid at ground floor level, applied to or set within the external walls and installed at roof level. We also apply insulation between floors and within internal partitions. Below is one of the typical sections from our detailed drawings. Our detailed drawings show sections through the building at different points to show detailed elements of the structure. The details are accompanied by notes which specify the materials, dimensions and other relevant information for both building control and contractors. 

  In the following posts we will give an overview of some of the main areas of importance with regard to providing solutions for whole house insulation, and also highlight the materials and techniques we will be employing to achieve a high standard of thermal efficiency.     

With foul drains pre-laid the internal walls are built up to floor level. 

A sand blinding layer is laid over the level fill of compressed hardcore.

With the damp proof membrane laid the ground floor insulation is cut and fitted to suit.

Another protective layer of  D.P.M is laid before the floor slab is poured and leveled.

With the slab now dry, work begins on the inner block skin.

Work continues on the ground floor block partitioning.

All joints between the thick slabs of insulation are taped and sealed. 

The build climbs towards the first floor.

From Dream To Reality

 

After discussions with our client it was decided that the new house would be of a traditional construction with rendered block cavity walls and an engineered truss roof. We wanted to achieve a  level of energy efficiency throughout the building that would be higher than the   mandatory standards set out in 2010. One of the main factors of an energy efficient building is to design and build in elements that guarantee a very low rate of heat loss. 

           
Reducing the rate of heat loss through the fabric of a building lowers the amount of energy required to heat the space within. While a key aspect in the effectiveness of an energy efficient building, conserving heat is not the only consideration. In our design we have specified a range of materials, techniques and technology which work together to reduce the overall consumption of energy and resources throughout the life of the building. Equally significant when building an energy efficient home is the control & quality of workmanship during construction. The design and specification alone will not guarantee a high standard unless followed through with a good quality build. From here we will explore each phase of the build from foundations to finishes to highlight how we have achieved the standards required for an energy efficient home and ultimately bring our clients dream to life.

Work on site commences with the demolition of the existing property.

Rubble is crushed for re-use on site.

After setting out, the new foundation trenches are excavated.

The footings have been poured and the first course of blocks laid.

  

So what is the ‘Code for Sustainable Homes’ ?

  

 The Code for Sustainable Homes is an environmental impact rating system for housing in England and Wales, setting new standards for energy efficiency and sustainability which represent important developments towards limiting the environmental impact of housing. The Code was officially launched on 13 December 2006, and was introduced as a voluntary standard in England in 2007. It complements the system of Energy Performance Certificate for new homes introduced in 2008 under the European Energy Performance of Buildings Directive, and builds on the most recent changes to Building Regulations in England and Wales. The code works by awarding new homes a rating from Level 1 to Level 6, based on their performance against 9 sustainability criteria which are combined to assess the overall environmental impact. Level 1 is entry level above building regulations, and Level six is the highest, reflecting exemplary developments in terms of sustainability.

The sustainability criteria by which new homes are measured are:
  

   •    Energy and CO2 Emissions – Operational Energy and resulting emissions of carbon
        dioxide to the atmosphere (both of which have minimum standards that must be met at
        each level of the code)

   •    Water H2O & Surface Water Run-off – The change in surface water run-off patterns as a
         result of the development– The consumption of potable water from the public supply
         systems or other ground water resources (each of which have minimum standards to be
         met  at entry level)

   •    Materials – The environmental impact of construction materials for key construction
        elements (no mandatory minimum standards).

   •    Surface Water Run-off - Management of surface water run-off from the development and
         flood risk

   •    Waste – Waste generated as a result of the construction process and facilities

        encouraging  recycling of domestic waste in the home (no mandatory minimum

        standards).

   •    Pollution – Pollution resulting from the operation of the dwelling

        (no mandatory minimum  standards).
 
   •    Health and Well-Being – The effects that the dwelling’s design and indoor environment

         has on its  occupants (no mandatory minimum standards).

   •    Management – Steps that have been taken to allow good management of the

        environmental impacts of  the construction and operation of the home

        (no mandatory minimum standards).

   •    Ecology – The impact of the dwelling on the local ecosystem, bio-diversity and land use

        (no mandatory minimum standards).

   In March 2008, the UK government announced a mandatory requirement for all new homes to be rated against the Code commencing May that year. No specific star ratings or assessments were set, but the rating meant that every new home owner knew whether their home was built to higher standards than building regulations and what standards had been met.

   In 2010 Code level 3 compliance became mandatory for public and private sector new-build residences, including flats and houses, effectively making redundant the use of code levels 1 & 2. Currently, compliance with higher levels of the Code is voluntary, with a long-term view for step-change increases. However, by making the information routinely available consumers are encouraged to be more demanding whilst also serving as an incentive for developers to consider building to the Code’s higher standards.

   Technical guidance is amended on a six-monthly basis, every April and October to reflect changes in materials and building techniques resulting from feedback from assessors and industry. There are also changes in the figures used relative to Approved Document Part L1A of the building regulations, for example the thermal standards set in Part L October 2010 make redundant the thermal standards of the Code for Sustainable Homes levels 1-3. This is representative of the Building Regulation's gradual improvement of thermal standards, level 4 Code thermal standards are set be part of the Building Regulations by 2013.

   The extra-over cost of building to Code Level 3, based on a building with a footprint of 100m² is valued between around £10,000-16,000, additionally the Code assessment costs around £2000 for a typical residential dwelling, the total cost of this is typically under 12% of a standard build. This includes such items as rainwater harvesting, solar thermal panels for hot water and electric. It should be understood that whilst the cost of developing to Code 3 and higher standards incurs the initial extra costs, substantial savings will be made in terms of the running costs, and importantly reduce the environmental impact both during construction and over the life of the building. 

 

After studying the plans we received from our client it was clear that there was scope to   maximize and improve the use of available floor area. On the ground floor we made adjustments to the west wing which allowed us to better proportion the guest bedroom and also allowed the inclusion of an en-suite. On the first floor we extended the layout into the previously redundant roof voids to give an extra room and improve the proportion of the remaining rooms.

 

Revised Scheme

Below are the elevations and plans after undergoing the revision stage, various aspects of the design were discussed with the client and alterations made until we arrived at the final proposal. This would be the final design, ready to be worked up into detail drawings for building control approval.

After revision the elevations have undergone some minor changes from the original drawing, but the style is still consistent with the original. Roof-lights have been added to the east elevation to give light and an escape route from an additional first floor room. The dormer cheeks have been widened to better accommodate internal window furniture and several windows have been given a deeper profile for extra light and are more suitably proportioned.

Original Plans

Below are the original layouts of the ground and first floors. The proposed property comprises of three bedrooms, bathroom and en-suite to the first floor. The ground floor comprises of an open plan kitchen diner with adjoining utility and mud room, together with a living area and further guest bedroom.

Form & Function

Before we could develop the structural design or material properties of the new house, we needed to fully develop the clients original drawings into an approved design which would  fully realize the clients  requirements in line with the brief. Below are the elevations taken from the initial design drawings.

 The design is similar in style to the existing property, essentially a white rendered dormer house with glazing to closely match the style of the original glazed units. It is clear from the drawing that the client had already intended on installing ‘P.V’ panels on the roof of the south facing elevation. ‘P.V’ panels should always be installed on a south facing roof if possible to ensure maximum solar exposure during daylight hours.

The Brief

Following a telephone inquiry, we made contact with our clients and arranged to visit them to find out how we could help them. During the consultation it became clear that our clients wanted to demolish an existing property, and in its place build an energy efficient home that would at the very least meet or preferably exceed the mandatory standards set out by the code for sustainable homes. Our clients presented us with initial drawings of their proposed dwelling upon which we would base the final design. The overall footprint of the new house was to be 100m², and of a similar style to the existing house.

Given present awareness for the need to conserve energy and resources, and encouraged by the economical benefits that can be gained, a growing number of prospective clients are exploring the possibility of building new energy efficient homes. We at David R Davies (Consulting & Architectural Engineers)Ltd, and our associates at Ashvale Contracting Ltd are learning and gaining more experience everyday of how to best design and build the next generation of energy efficient houses. It is not only residential properties that we are helping to develop, every type of building can be designed and built to save energy, and function with less strain on resources.

  For this case study we will follow the development of our clients energy efficient home, to illustrate the process and highlight some of the technologies and methods we have employed in order to realize their dream.