In this article we cover:
- Details of mass timber extension costs
- Cottage configuration and reasons for extending
- Decision to build without concrete
- Building the mass timber extension
- Energy efficiency
- Screw foundations, including costs
- Securing planning permission
- Direct labour tips
- Lime plastering
- What DIY they did
- Tips to others, favourite features
- Specification and timeline
- Before and after floor plans
- Suppliers and professional photographs
Overview
House size before: 60sqm
House size after: 80sqm (replaced the 20sqm extension with 40sqm)
Bedrooms: 2
Plot size: 100sqm
Heating and ventilation: Air to air heat pump
Build method: Solid wood
Cost Breakdown
Total cost: €166k of which:
Demolition costs: €75k
Builder cost (rounded): €91k comprising:
Pile (screw) foundation: €5k
Glulam timber structure build: €40k
Insulation, cladding and roofing (ready for green roof): €20k
Windows: €9k
Kitchen: €5k
Electrician: €4k
Plumber: €3k
Heat Pump: €5.4k
When Christina and Duncan Jones set out to improve their 200-year-old protected cottage on a tight urban site in Co Dublin, they chose a radical but careful solution: a modern, light-filled addition that preserves the building’s history and floats on screw foundations.
Christina and Duncan’s 1890s property is listed on the Record of Protected Structures, located on a very tight urban plot in a Dublin conservation area hemmed in by neighbours on both sides and a high retaining wall on the rear boundary. Compact and modest in scale, the original house consisted of a living room, two small bedrooms and outside wc.
Due to its unusually high ceilings, the space was very dark and its form remained largely unchanged for over two centuries. Except for the back yard being roofed-in to make a kitchen and bathroom. Like many cottages of its era, it had been extended at some point, but not in a way that served modern living particularly well.
“The old rear cinder block extension housed the kitchen and project supplier bathroom, and it was extremely poor quality: single block walls, felt roof, cold, leaky, tiny and with poor drainage,” explains Christina. “
We lived with that for 10 years, fixing bits here and there, but we never invested too much because we always knew we’d eventually have to take it down and start again.”
Their long-term plan finally took shape when they hired an architect to survey the existing property and prepare a design to tackle the house’s problems. “Even though it was a small extension (40sqm), we had to have an architect draw plan to apply for permission because of its protected status,” explains Christina.
Evolving plan
The initial plan was simple. “It was really to just have a kitchen and bathroom that were warm and waterproof,” Christina says. But as they looked at how the old cottage fit with its surroundings and how the extension could improve the flow, they saw a chance to rethink how they lived in the space.
The new extension links directly through what once served as the cottage’s back door. “You come in the front door, cross the original living room and step through that old threshold,” Duncan says. “Suddenly you’re in this bright, open area where everything feels connected.”
The kitchen is on the left, compact but well designed. Straight ahead is a spacious new lounge, with a sliding door to the bathroom. At the back, large, glazed openings frame the small piece of garden – only a metre and a half deep after construction but still bringing in greenery and sunlight.
“It was absolutely worth losing some garden for decent living space,” Christina says. “We don’t miss it at all.” Because the house is listed, there were clear design limits, especially on how the extension should look next to the original cottage. Conservation rules said the new structure had to look different from the original cottage. “We briefly thought about matching the old style,” Duncan admits, “but planners shut that idea down immediately.
They were very clear; it couldn’t mimic the cottage. It had to look modern.” The architect’s design included a mono-pitch roof as the logical solution for the extension, allowing it to look clearly contemporary while also addressing site specific challenges.
“There’s a tall boundary wall which is also protected as part of the original structure,” Christina explains. “We couldn’t change that, so we couldn’t install windows to the side of the extension.”
Since the extension also faces north, they had to carefully consider how to bring in as much natural light as possible. “The monopitch roof rises up to give us a double height elevation in which we installed a high-level tranche of clerestory windows above the kitchen.
The roof angles down to the rear where we have glazed doors and tall windows opening on to the garden. This configuration was crucial for getting light in.” South-facing, it permits passive solar gain while avoiding casting a shadow on the remaining garden and neighbours
Q&A With Duncan and Christina
What is your favourite design feature?
Duncan: The light in the extension with the mono-pitch roof. On a sunny day you can not only see the light, but even the weather patterns rolling across the roof. Also, we can see the moon. The warmth and lack of draughts are huge improvements.
Christina: The living space is so much more comfortable. Before, rooms were cold, damp and we were fighting slugs. Now, even though we lost a bit of garden, we have a bird feeder we can see from inside, sky views and room to sit together.
What surprised you?
The laminated timber frame went up so quickly and cleanly. Three guys, hand tools, up in two weeks. No mess, no drying time. It was far better than expected.
Would you do it again?
Duncan: Pretty much, yes. A lot of work, but the house is so much better. The old kitchen and bathroom were so hard to live with. Worth every bit of the trouble.
Christina: You have to be willing to live with hardship and especially uncertainty, but the end result is hugely rewarding.
Concrete free
The architect designed for timber frame from the outset. “Traditional block construction would have been clearly unsuitable, not least because the cost of a block build was going to be more than we paid for the house,” Duncan says. “And the site is very tight, so we had to research alternatives; that’s how we landed on timber.”
That research led them to an engineered structural timber, glulam. “Basically, all the timber bits were cut and glued together in a German factory and then sent to us by truck, like a huge flat-pack kit. It really did feel like an IKEA manual,” Duncan explains. “Just on a massive scale.” An Irish supplier translated the architect’s drawings into a detailed construction package and carried out the assembly on site. Duncan would advise talking to your timber frame manufacturer early. “The company will have lots of experience and contacts,” he says.
But the biggest departure from tradition wasn’t the timber. It was the absence of cement. Instead of digging foundations, a risky undertaking near shallow, centuries old walls, the entire extension floats on steel ground screws. “Neighbours told us horror stories about previous digging works which had ended up destabilising their own walls or next door’s,” Christina says. “We didn’t want to take that risk.”
Instead, the giant screws, driven deep into the soil, provided a safe, stable base with minimal disruption. Ground screws also meant the mains water line and sewerage pipes that run under the extension wouldn’t be disturbed, as there was no need to dig foundations and no extra weight was placed on the ground above them.
Installation was surprisingly straightforward. “They’re between one and a half to two metres long, depending on the ground conditions beneath,” Duncan explains. “We have 20 screws in total.”
Cost was relatively modest. “It was just under €2,000 for all the screws, plus labour,” he says. For Christina, the decision was also about protecting the existing cottage. “ We hired an independent engineer to check the screw foundations after they were installed,” Duncan says. “He signed it off as being well above required strength.” Planning authorities weren’t only concerned with how the extension looked. They also needed assurance that construction wouldn’t disrupt the ageing sewerage lines running beneath neighbouring properties. Managing rainwater was a particular focus.
The couple opted for a green roof on the new extension – not because planners demanded it, but because they wanted a softer, more sustainable way to deal with rainwater on their tight urban site. The build-up is a lightweight, layered system: a plastic mesh tray filled with clay pebbles that store water, topped with a coconut-fibre mat pre-planted with sedum. They had no say in the exact planting mix – the installer used a standard sedum blend know to work well in Dublin. But they’ve been told the roof will slowly naturalise as birds drop seeds and other plants take hold. Their remaining challenge is extending this system over the entire 22-degree mono pitch: finding someone willing to install a green roof on such a small, pitched domestic project is proving difficult.
Tips
Plan far ahead and line trades up to avoid the project sitting half-done while you wait for the next step. We should have researched more between phases for sure.
Design the outside, not just the inside, before demolition/ groundworks happen. We wish we’d given proper attention to what we’d do with the garden. Use breathable materials, opting for lime-based plasters, not cement, in old solid-wall houses.
Keep an open mind. Go in expecting disruption and uncertainty, but keep sight of the end result.
Close quarters
Because access was tight and there was no space for heavy machinery, much of the work had to be done by hand. Demolishing the old extension took three workers a week. It was slow, hard work and cost more than using machines, but there was no other way.
Delivering the glulam structure took careful planning. “The trucks had to come at 6am to avoid blocking school traffic,” Duncan says.
Maintaining good relations with neighbours was essential. “We had to keep them informed and sometimes depended on them for parking,” he says.
They kept living in the cottage during the work, which made daily life feel a bit like camping. “We had no water for stretches,” Duncan says. “We joined the gym just to use the showers. And we had an outdoor toilet for a while. It was rough, but we managed.”
One of the best things about the new timber clad extension is how well it keeps in heat. All the windows are triple-glazed and the insulation is thick and carefully installed. The couple haven’t applied for a BER rating, but the improvement is dramatic. “The extension just feels warm in a way the old one never did,” Christina says. “It’s comfortable all the time.”
This builds on earlier upgrades to the original cottage. Prior to the extension, the couple removed the gas central heating system, added hempcrete insulation to the walls and put in an air to-air heat pump.
The heat pump keeps both the old and new parts at a steady, comfortable temperature. Inside, the design is “simple, honest and easy to maintain.” The couple kept the kitchen design deliberately modest and bright. “We went for simple, straightforward stuff and all light colours,” they explain. The worktops are a fake marble laminate while the kitchen walls are painted a warm yellow.
The kitchen itself is custom designed and fitted: they had it measured, planned on computer, and then installed as a made-to-measure set of units. A key principle throughout was to keep services as simple and visible as possible. “There’s a minimum of water pipes in the house,” they say. “It’s literally just the water to the sinks and the toilet and shower. So if anything goes wrong there, we will see it immediately.”
The new bathroom is accessed off the living space via a sliding door Duncan made himself from OSB and painted with an underwater fish scene for a splash of colour. Inside, the bathroom is kept just as unfussy as the kitchen – mostly white, straightforward fittings, chosen with reliability and easy maintenance in mind rather than trend.
The lighting is simple but works well. Round fixtures light up the kitchen and bathroom, while uplighters in the lounge reflect light off the sloped timber ceiling, making a soft, pleasant glow. Outside, the landscaping is easy to care for and helps manage water. Stone chippings stop weeds and let rain soak in naturally. Pots of flowers and water butts add greenery and make the small backyard practical.
Hands on
The couple took charge of hiring the trades and did as much as they could themselves to save money. “Be as available as you can during the build, so decision making is quick. You’ll pick up Ground screws being installed on how things are going and can fix issues before they build up,” advises Duncan.
“We knew everyone well by the end,” adds Christina. “Good communication meant even if there was a problem, like a cost overrun, we could sort it out together.”
What they didn’t expect was how the extension work would expose hidden issues in the original cottage. Stripping back the cement layers revealed cracks, damage and even plastic bags stuffed into wall cavities by long gone builders.
A stonemason fixed part of one wall, but there was still a lot to do. Hiring experts for everything was too expensive, so the couple did much of the work themselves. “We took a class with Dun Laoghaire County Council on maintaining period houses and learnt how to plaster via YouTube videos,” Christina says. “Our first project was to apply hempcrete insulation and lime plaster in Duncan’s mother’s house in the UK.”
“It was exhausting but empowering,” adds Duncan. “We ended up fixing so much ourselves.”
Delays also tested their patience. Waiting for the windows meant the extension was open to the weather longer than they planned. More than once, they had to sweep out rainwater by hand. But they both agree the lessons were worth it. Now, they understand their home much better: how it breathes, how it’s built and what it needs. Today, the new extension doubles the size of the cottage without taking away its character.
The old cottage is still dark, historic and full of texture, while the new part feels bright, spacious and truly modern. The two parts don’t compete; they work well together.
The result is a home that respects two hundred years of history while giving Christina and Duncan the comfort and sustainability they always wanted. It’s warm, dry, full of light and fits the way they live today.
