Building and living in a Passive House -Why did we build a Passive House?
Approaching retirement, we lived in a lovely village far from the support services we might need as we age. So, I searched, and found, a house for sale in an appropriate location and asked my husband to view it. He went to the wrong house! But he arrived home excited about demolishing it to build one to our own design. Serendipity?
This blog about building and living in a Passive House, is written by Linda Shall, a volunteer with Sustainable St Albans. Linda lives in Harpenden with her husband and cats! Linda is also giving an online talk about her experience of the Passive House on 23 June – requires booking.
I recently graduated with a BSc in Environmental Science and learned that running a Passive House emits much less carbon dioxide than conventional ones. We investigated this environmental sustainability claim…demolished the ‘wrong’ house…and built one of the earliest Passive Houses in Harpenden. We moved in a whisper before Lockdown One! So, what is passive about a Passive House?
What is ‘passive’ about a Passive House?
A Passive House is one that becomes and remains warm enough for human comfort all year round, without using an ‘active’ space heating system that is likely powered by fossil fuel. We have NO boiler, NO radiators.
In essence, a Passive House captures the energy in sunLIGHT (not heat) entering through its windows, converts it to heat for circulation around the building; along with heat emitted by human and animal bodies, domestic appliances, computer equipment, hot water, cooked food etc…
What are the essential basics of a Passive House?
They are –
- insulate, insulate, insulate!
- draught-free construction
- high-performance windows and doors
- mechanical ventilation and heat recovery
There are no prescribed building products to achieve Passive House standards. Consequently, all Passive Houses do not look the same and are not built using the same materials.
What matters is that the detailed performance requirements in the Passive House Planning Package are fulfilled to achieve the mandatory comfort, health and energy standards for certification by the Passivhaus Institute in Germany. A straw house could be a certified Passive House if it meets the standards!
Insulate, insulate, insulate!
For buidling and living in a Passive House, insulating the outside walls, roof space and beneath the ground floor is essential basic #1 for a reason. Often, Passive House outside walls are 450-500mm thick compared to new conventional cavity wall thicknesses of 250-300mm. Ours comprise several empty and filled cavities, waterproof membrane and myriad insulating materials, to prevent inside heat and outside cold from moving through the walls.
Our house sits atop an underground c300mm thick polystyrene raft to prevent heat leaching into the ground. ‘Whoa! Plastic?’ But I contend this is where plastic is the best material, and lasting around 200 years is hardly ‘single-use’…
What’s not to like about the reduced carbon dioxide emissions due to the:
- absence of warm/cold air leaking outside/inside the house
- reduction in outside traffic noise penetration through thicker walls?
Draught-free construction for a Passive House
We applaud the heroic properties of ‘line of airtightness’ tape used throughout the house. It hermetically seals joints between any two materials. It is so much more than duct tape that dries out, cracks and bubbles over time.
Other draught prevention solutions include no metal cold ‘bridges’ through outside walls eg nails, screws, brackets, ties, mesh etc. Borrow Sustainable St Albans’ Thermal Imaging Camera to find them!
What’s not to like about the reduced carbon dioxide emissions due to the …
- permanent absence of draughts
- constantly warm temperature everywhere?
Passive House high-performance windows and doors
We are enthralled by the properties of Passive House windows and doors. Although not a prescribed product, they help achieve Passive House standards more easily.
What’s not to like about the reduced carbon dioxide emissions due to the …
- high G-value triple-glazing that captures and keeps more solar energy than standard window glass
- fine-tuneable hinge/locking systems to pull windows and frames closer together?
BUT… We do acknowledge the challenges presented by keyholes and cat-flaps!
Mechanical ventilation and heat recovery – MVHR
In a conventionally-built house, internal air turns over between 6-15 times PER HOUR which means that it needs to be warmed 6-15 times PER HOUR for comfortable living. Because of our superior insulation plus draught-free construction plus high-performance windows and doors our internal air naturally turns over only ONCE EVERY 3 HOURS.
Consequently, we mechanically ventilate our house to keep the air fresh, dry and warm. MVHR technology transfers 95% of the heat in stale, damp air extracted from bathrooms and kitchens and transfers it to fresh, filtered incoming air for circulation around the house by a low 35w/hr fan (saving ten times the amount of energy it uses).
What’s not to like about the reduced carbon dioxide emissions of constantly fresh air that is warmed passively by sunlight and heat emitted during the normal running of the fridge, freezer, TV, hairdryer, computer, shower, humans and pets etc.
So – does building and living in a Passive House live up to billing?
Ours does! Building and living in a Passive House has set new sustainable standards for us. We have no draughty room corners, windows or doors; we set our preferred temperature per room – bedrooms cooler than living rooms; incoming air is filtered against air-borne pollutants; we suffer much less noise penetration from road and air traffic.
We prevent overheating in summer by shading windows using an array of external blinds, louvres, an awning and hit-and-miss cladding over smaller windows.
Of course in winter, heat is not created from sunlight inside the house when window blinds are closed, nor is it emitted from most domestic equipment when we are away from the building. Consequently, when returning after a few days’ absence it takes the air a few hours to reach our preferred temperature. It would take less time if our household comprised more people, as we resumed operating heat-emitting equipment around the house. Because we could, during the build we installed a small air-pump for occasional use, which we have used a few times on these occasions. We also installed under-floor heating for emergency use in the lounge, which we have NEVER used!
Finally…the building cost of a Passive House
Yes, the capital cost per m2 is higher than for a conventional house. Recent estimates state c7% depending…. this concentrated our minds on how many rooms we actually need. We had 14 rooms, now we have 10; overall square meterage is down 18%. We compensated for the extra capital cost by building a smaller house more suited to our lifestyle needs.