Nobody thinks about the water tank until it's 2am and there's a rhythmic thumping from the ceiling.
Most Dublin houses have a cold water tank in the attic. When you convert the attic, the tank needs to be relocated - usually into the storage area behind the knee walls. This is completely standard and every builder does it. But where exactly it ends up matters more than you'd think, and I learned that the hard way.
The basics
The cold water tank feeds your taps, shower, and toilet cisterns via gravity (or via a pump in some setups). During a conversion, the builder moves it from the main attic space into the storage area so the living space is clear. The tank gets reconnected to the existing pipework, the ball valve keeps it topped up from the mains, and everything carries on as before.
The relocation itself is straightforward. The issue isn't whether it gets moved - it's where it ends up and what's directly below it.
What happened with mine
I hadn't given a moment's thought to where the water tank would go. The builder moved it to the storage area, which happened to be directly above a bedroom. Seemed fine at the time.
The problem only became obvious once we were living with it. Every time someone showered, flushed a toilet, or ran a tap, the tank level would drop and the pump would kick in to refill it. My house - being a newer build - came with a submersible pump inside the tank. And it was loud. A low, rhythmic thumping that transferred straight through the joists into the bedroom below. At 2am after someone uses the bathroom, it's not what you want to hear.
I tried to fix it. First I put rubber matting and insulation under the tank to dampen the vibration. It helped a bit, but not enough. In the end, I got a local plumber to replace the submersible pump with an external pump - a quieter unit mounted outside the tank. That solved it. But it was an additional cost and hassle that I could have avoided with a bit of planning.
Two things happening at once
I was unlucky in that two problems combined: the tank was positioned above a bedroom, and the existing pump was cheap and loud. Either one alone might have been tolerable. Together, it was a real nuisance. In hindsight, the conversion was actually a good time to replace the pump - while everything was accessible and a plumber was already on site.
The lesson - position matters
The takeaway is simple: think about what's below the storage area where your tank will sit.
Avoid positioning the tank above a well-used bedroom
If you have a choice of which storage area the tank goes in, pick the one above a bathroom, hallway, or less-used room. The pump noise may be barely noticeable during the day, but it’s a different story at night.
Balance position with practicality
The tank position needs to make sense for the plumbing — you don’t want excessively long pipe runs. But within the practical options, picking a location that avoids bedrooms below is worth the conversation with your builder.
If your pump is already loud, now is the time to replace it
If you’ve noticed your pump being noisy before the conversion, the build is the perfect opportunity to swap it out. Everything is accessible, a plumber is on site, and you’ll avoid the hassle of doing it later.
Ensure good access to the tank
You may need to service the tank, the ball valve, or the pump in future. Make sure the storage hatch gives you proper access — not a tiny gap you can barely fit through.
Hot water supply - check where yours comes from
One thing that surprised my builders was that my hot water supply came from the ground floor, not the first floor. Most Dublin houses have the hot water cylinder on the first floor (in an airing cupboard or similar), which makes it easier to run pipes up to the attic. Mine was on the ground floor, which meant longer pipe runs and a bit more complexity.
This isn't a showstopper - it just needs to be identified early so the plumber can plan the routing. Our ensuite waste pipe and plumbing guide covers how pipes are typically routed during a conversion. Run through your hot water setup with the builder before the work starts. If your cylinder is on the ground floor, flag it - they may not have encountered it before and it's better to discuss it upfront than discover it mid-build.
The bottom line
The water tank relocation is a standard part of any attic conversion. But "standard" doesn't mean you shouldn't think about it. Ask your builder where the tank will go, consider what's below that spot, and if your pump is already noisy, use the conversion as an opportunity to replace it while everything is accessible. While the plumber is on site, it's also a good time to plan your attic radiator and heating setup.
It's a small detail that makes a big difference to how you live with the finished space - especially at 2am.
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