Detailed guide – planning a low energy refurbishment

Terraced houses - typical candidates for planning retrofit improvements

Whole house retrofit planning takes time to do properly, and involves several stages prior to being able to start on the actual building work. Below, we explain a bit more about what is involved.

The first stage – determining your existing energy situation

Before being able to plan specific targets related to improved comfort, reduced energy consumption or carbon emissions, we need to know where your house stands now in terms of energy demand and carbon emissions. This baseline study highlights the main culprits in terms of heat loss, which vary depending on the type of house and its structural properties.

The second stage – making a plan of retrofit improvements

Using the baseline as a reference point, it is then possible to look at what can be done to improve those areas of heat loss given your own specific targets for reducing energy demand or carbon emissions – again, what can or should be done will vary depending on the type of house. This is followed by practical aspects such as ventilation design, comparing the estimated cost of the work to your available budget, and thinking about the sequence of tasks for the project.

Improvements can be implemented in a phased approach over several years if needed, although this can introduce complications for certain tasks, especially airtightness. However, this may be the only practical way forward for some homeowners – yet the principle of analyzing the existing situation and making a plan of improvements for the whole house is the same as if you would do the work in one go. For those who would move house before completing the work, the action plan could quite easily be handed over to the new owners.

The analysis process – more details about these two stages

The likely sequence of events during these two stages is outlined below.

  • An on-site consultation visit at your house may be a practical first step. This allows discussion of what would be likely in terms of retrofit – such as the largest probable areas of energy loss, as well as practical considerations of carrying out major refurbishment work. It also enables us to flag up any glaring energy-related issues that you could fix in the meantime.
  • If you engage ColdProof to carry out the analysis, we will then undertake a detailed survey of the whole house, resulting in floor plans and elevations. This survey can take some time as there is a fair amount of additional detail to gather including ascertaining the exact make-up of walls and junctions, investigating crawl space dimensions and joist moisture content, measuring external window reveal depths, and estimating external shading objects like buildings or trees. We will need access to the the crawl space under any suspended floor, as well as the loft.
  • Using the survey data, we will model the energy demand of both the existing house and an improved scenario using the Passive House Planning Package (PHPP), a tool that is proven to give accurate predictions in terms of both carbon emissions and energy consumption. The existing situation will vary depending on your house’s specific characteristics and its location, and the improved scenario will be based on specific space heating demand or carbon emissions reduction targets that we would agree on (for example we will normally try to aim for an overall space heating demand of 40 kWh/m2/year and carbon emissions level of 22 kg/m2/year, which might equate to around a 70% reduction depending on the original situation). Part of the data entered would would include air leakage data from an initial fan test, data on heat loss or gains from thermal bridge models, and some data on ventilation design – see below.
  • Actual air leakage data will need to be acquired through a blower door fan test, carried out by a ventilation testing specialist. This is to find out how leaky your house actually is, with test result data being fed into the PHPP model. We often try to coordinate this test with when we are on site for the detailed survey stage.
  • Example breakdown of space heating savings using PHPPExisting thermal bridges will be modelled using THERM, and any heat loss or gains will be added to the PHPP model. Modelling these areas of cold bridging means that heat loss and low surface temperatures can be reduced or designed out at problem junctions in the proposed retrofit – typical areas that need modelling in a retrofit are party wall junctions (floor, loft, external wall).
  • The Mechanical Ventilation with Heat Recovery (MVHR) system will then need to be designed in detail, which includes calculation of air flow rates, specifying which MVHR unit to use and its location within the house, looking at duct runs and finalizing materials needed. Some of this data will feed back into the PHPP model, while also informing us of costs and practical installation considerations.
  • The next stage will be to specify materials and estimate costs in detail for everything in the project. Cost will include improvements related to energy efficiency, but also other tasks that need doing but which are not related to energy efficiency, yet which will nevertheless add to your overall budget (e.g. new kitchen or bathroom, knocking walls through, plastering and painting). When all costs are added up, along with a contingency factor, this allows us to predict the real costs of going ahead with the retrofit. This may then require that certain materials and costs are adjusted based on the available budget, which in turn will again will require the modification of the PHPP and thermal bridge models where applicable.
  • As part of the cost analysis, we can also look to engineer any of the energy efficiency improvements for cost-effectiveness through an economic analysis. This is where energy savings of individual improvements are compared to their implementation costs, and can show payback periods for the whole job and per improvement. The idea is to arrive at the most cost-effective way to allow you to reach your energy or carbon reduction targets.
  • Example breakdown of carbon savings using PHPPOnce we are on target regarding proposed energy improvement and cost, the next stage is to make a work sequencing plan which outlines what tasks need to happen before others.
  • Throughout the whole process, there will be ongoing discussion with you of the results as they develop. When everything is finalized, we will meet again in person a second time to go through the results. What you will be left with is the overall cost analysis (as an Excel spreadsheet), SketchUp models and thermal bridge models.
  • Finally, we can also assist with providing ongoing advice for those carrying out a retrofit, as well as project coordination if required, either full-time or part-time.