Old English narrowboat Mermaid, next to the fully-retrofitted British Barge, Penny Lane
Image: Jay Ramsey
Houseboat retrofit demonstrates the power of insulation
When period-home insulation surveyor Jay Ramsey upgraded his houseboat, he decided to put everything he knew about energy saving to the test. He fitted his new boat with the level of insulation and ventilation recommended for a full listed-property retrofit. The results were “incredible!”.
Carbon Savvy: Can you tell us about your houseboat project?
Jay Ramsey: Sure – our first boat, Mermaid, was an English Narrowboat. She has rudimentary insulation and secondary glazing, and a small woodburning stove. Charming, with efficient use of space, Mermaid has been our family home for ten years. Now our two girls are approaching their teens, we wanted more space and separate bedrooms. After a long search we found Penny Lane, a 1980s British Barge three times the size. While renovating her we took the opportunity to fit modern levels of insulation along with mechanical ventilation and underfloor heating.
Lounge-dining room on the retrofitted houseboat
Image: Jay Ramsey
CS: What insulation do the two boats have?
JR: I fitted-out Mermaid 15 years ago with an average of 40mm polystyrene boards, but they are loose with air gaps around. Later I added perspex secondary glazing with a 50mm air gap. Her woodburning stove also powered underfloor heating. We were always warm and cosy on board, but in the winter the internal temperature dropped a lot at night and we had to open and close windows a lot to balance warmth with fresh air. She used a lot of logs, which was hard work to source, season and store.
After working as a surveyor for the period home insulation company Mitchell & Dickinson for ten years, I knew the optimum level of insulation in the UK is 300mm of sheep wool or equivalent. So I insulated Penny Lane with closed-cell spray foam to a thickness of 100mm on the walls and ceiling. The floor has 100mm PIR Board covered by 80mm of concrete and underfloor heating, for which pipes are laid in 20mm polystyrene boards. The concrete forms 14 tonnes of thermal mass which helps keep a steady temperature inside the boat. The windows are UPVC double-glazed with a 16mm air gap, which fulfills modern building regs for a house. The bottom 200mm of the walls is below the waterline, and insulated with 200mm sheep wool. Since closed-cell spray foam and PIR board have approximately twice the efficiency of normal insulation, Penny Lane effectively has 200mm of insulation all round.
Double bedroom on board a low-carbon houseboat
Image: Jay Ramsey
CS: Can you describe the ventilation in the two boats?
JR: Mermaid has passive ventilation, in the form of permanently open vents in the roof and end walls. Since we had a gas stove and wood-burner we needed open vents for the safety certificate. Penny Lane has no gas and the wood-burner has a room-sealed vent ducted directly outside so we don’t need open vents for safety. Ventilation then becomes purely for human comfort and managing humidity.
We chose to fit single-room heat-recovery fans. The way these work is that the fan blows your warm, stale air out through a ceramic honeycomb, which warms up. After 70 seconds the fan changes direction and brings fresh air in, which passes through the honey comb and heats up, so you get warm, fresh air into the room. They are 80-90% efficient, which means that you are capturing a lot of the heat that you would otherwise be losing. In the kitchen and bathroom the units have two fans, so they can move twice the volume of air, with the same heat-recovery principles.
The fans have different speeds: Low speed is very quiet, which is fine for sleeping, and high speed is like a bathroom extractor fan. The fans in different rooms are in sync and work together to pass the air throughout the whole room rather than just a small section of it. They can be set to come on when room humidity is high. They also have an “open window” button, where they come on at full power for half an hour – just like opening a window for half an hour, but without losing the heat.
Internal face of the single-room heat-recovery ventilation
Image: Jay Ramsey
CS: Amazing. What are the names of the fans?
JR: The type is a “single-room mechanical ventilation heat recovery” (MVHR) and there are lots of brands. We chose Blauberg Duo for the kitchen and bathroom, and Blauberg Midi for the bedrooms.
CS: Do you know what the annual running cost of the ventilation system is?
JR: The published energy consumption of each fan is 1.4W, which translates to around £6.50 per year for each unit. So that’s under £50 a year for the whole system, which is a tiny fraction of the cost of the heat that they save.
CS: How did the energy use compare between the two boats?
JR: On Mermaid we used 6 cubic metres of logs per year. We have been on board Penny Lane for just under a year and have used about 2 cubic metres of wood. This is remarkable when you take into account that Penny Lane is roughly three times the size of Mermaid.
CS: What is the difference in the living experience?
JR: It was a lot of work on Mermaid just processing that much wood. We needed six cubic metres of wood for this year and six cubic metres of wood seasoning for the following year, all stored carefully in fresh dry air, and I had to time all that work with the seasons and the floods. So from that point of view, it is incredible.
There is a stability in the atmosphere in the new boat which wasn’t there in the old boat. On the old boat we could get lovely and warm but it would cool down pretty quick when the heating went off. To have enough ventilation I slept with the window open but that became cold for other people, so we had those kinds of niggles. On Penny Lane there is just a constant level of warmth that is not fluctuating wildly depending on whether you forgot to keep the burner alight. It is also a lot cooler in summer.
Single bedroom on board a low-carbon houseboat
Image: Jay Ramsey
CS: Are there any disadvantages?
JR: Not really, but it is a slightly different way of using a space. For example, it’s a new approach to when to open windows, since that loses heat. And when you go into a room, instead of just a light switch there are also controls for heating and ventilation. The fans don’t take much maintenance but you do need to clean the filters every three months.
CS: How happy are you with the new system?
JR: It is just amazing how easy it is, how little time you have to think about the heating, and how little energy it takes. I’ve never lived in a well-insulated property before. There has always been the theory of insulation but too many drafts. A steel boat is very much a sealed unit – the only holes are windows and doors and ventilation openings. Although the insulation is not as thick as you might put in a larger house, because we had to balance insulation and space, it is fitted really well with no gaps and no thermal bridges. We were warm enough on the old boat but it takes a lot less effort to get there and the temperature is a lot more consistent. Overall, it’s incredible!
Results: Carbon Savvy calculated the size, energy use and CO2 emissions for the two boats. Penny Lane’s floor area of 128 square metres (sq.m) is 2.9 times that of Mermaid at 44 sq.m. Her internal volume of 264 cubic metres (cu.m) is 3.4 times larger than Mermaid at 78 cu.m. Yet after a full retrofit Penny Lane used only a third of the energy of Mermaid. Taking into account that Penny Lane is a 3.4 times larger space, the heating energy she uses per cu.m is one tenth that of Mermaid. This demonstrates that a full retrofit with insulation levels close to (but below) those recommended for a period home retrofit, when combined with MVHR ventilation, can achieve no less than a 90% reduction in energy use.
Thanks to our sponsors Mitchell & Dickinson for collaborating with us on this post. If you are interested to find out more about getting your period home professionally retrofitted, visit their website at www.mitchellanddickinson.co.uk.
Finally, a huge thanks to Jay Ramsey for sharing this amazing story, which we hope will inspire many retrofit projects.
Wishing you a cosy home this winter,
Mukti and the Carbon Savvy Team
