Designed for the planet
PH15 reduces all carbon, both operational and embodied. We follow all the guidlines of the UK Climate Change Committee for NetZero. Our system uses LVL timber to minimise waste and maximise recyclability.
PH15 is a housing solution in line with the UK Climate Change Committee (CCC) guidlines for NetZero1. PH15 deliveres NetZero ready houses in a simple and cost-effective format, an approach commonly termed Fabric First.
The CCC has identified that we need to move towards constructing more homes using timber and timber products. For PH15 this results in an embodied carbon reduction of over 70%. This compares a PH15 timber frame with a conventional masonry build. We do not include the carbon sequestered in the frame and insulation.
Why not?
You may see claims for timber framed houses that they are carbon neutral or even carbon negative. Indeed there is a wide spread belief in the timber industry that timber is a carbon neutral material. We disagree. Building a house out of timber does not in itself sequester any carbon. This carbon has already been sequestered beginning 60 odd years ago when the trees harvested today were planted.
While it is certainly true that the timber in buildings can lock up the sequestered carbon for a long time (especially if we design
1 NetZero in use. The targets and methodology proposed for UKNZCBS closely align with the operational energy and renewable energy generation targets of the Passivhaus Plus standard
for longevity) harvesting trees for building releases carbon over a short time scale. Over 30% is left in the forest as roots and trimmings which decomposes. 5-10% may be lost to the stripped bark which is often burnt for power and depending on the use the log is put to, more may be lost at the processing stage where timber that is too small for construction is pulped for short lived paper and card products2. Any new planting has to over come this deficit before we can say that we have increased the carbon sequestered in our forests.
So what can we do?
We strongly believe that if we are to build more homes with timber instead of high embodied carbon concrete and steel, we have to use it more efficiently than we do now. Using as much timber as possible in the mistaken assumption that more carbon is being sequestered is wrong and actually harmful. A move toward more timber framed buildings that use solid section timber will use up our timber resources faster than they can be replaced and short term carbon emmissions from forestry may then be adding to atmospheric CO2 faster than new growth is removing it – at least in the medium term.
2 Tim Searchinger, Liqing Peng, Richard Waite and Jessica Zionts – Wood Is Not the Climate-friendly Building Material Some Claim it to Be – World Resoures Institute July 20, 2023
How is PH15 different?
The PH15 frame uses small section LVL I-joists which make much better use of timber and produces a product that is stronger and more stable than solid timber of the same size. Sawdust and chips that could go to waste are converted to insulation products.
We then design the system to use the I-joists as efficiently as possible. A PH15 frame can constitute as little as 15% of the whole with 85% being insulation. Cutting the frame off-site minimises wastage as the cutting software can maximise the number of required pieces cut from the LVL stock. This means timber resources go much further and reduces the pressure on our forests to produce bigger and bigger harvests. You also benefit as you get a super insulated home.
We are also actively looking to replace some of the timber based cavity insulation with hemp. This super-crop yields three to four times more usable fibre per hectare per annum than forests, and hemp does not need pesticides or herbicides. Hemp has a much faster crop yield. It takes about 3–4 months for hemp stalks to reach maturity, while trees can take between 20 and 80 years and therefore it has a usable annual CO2 sequestration which could be directly off-set against emmissions.
Trees help to clean our air, reduce flood risk, provide homes for wildlife, store carbon and have been proven to boost our own health and well being.
On average a tree can sequester around 25kg of CO2 a year so a tree planted in 2024 could therefore remove 0.65 tonnes of CO2 from the atmosphere by 2050. UK forests only cover 13% of our land area. We now urgently need to plant trees (the estimated need is 1.5 billion new trees by 2050) to help meet our climate targets.
We contribute1 to the Woodland Trust and Woodland Trust Scotland for the planting of trees, to cover the amount of CO2 to produce each PH15. The Trusts plant and maintain native species woodlands that helps to maintain existing biodiverse eco-systems and create new ones.
1 Based on the MOREwoods scheme where as of summer 2024 the estimated cost of planting a tree is around £2 plus.
We do not claim that the CO2 is fully offset by this action as there is no guarantee of future growth rates or survival but it is our hope that it does make a useful contribution to maintaining and increasing native woodland. The metric we use is the planting of 1.5 trees per tonne of CO2 released.
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