THIS HOUSE has one of the best views in Dublin: a porthole frames a picture of Howth; a rectangular opening captures a Martello tower but there are also huge windows and terraces from which to enjoy the complete sea scene, including Dalkey island.

Visitors can see this for themselves on Sunday October 11th between 12pm-5pm as part of the Open House weekend (you need to book in advance).

This is just one of the buildings not normally open to the public which form part of the fourth annual Open House Dublin weekend (running from Thursday October 8th to Sunday October 11th). The following weekend marks the first such architecture-fest in Galway (October 16th-18th).

This year the Dublin event has expanded to include 160 building tours, events, talks and workshops. Normally private buildings that will be open include architects’ offices, government buildings, the Irish Times building and the Elm Park estate – plus you can get in free to places that normally charge an entrance fee, such as the Guinness Storehouse and Trinity Science Gallery.

A number of architecturally interesting houses are also opening their doors, such as Lis-na-Carrig in Dalkey. The expansive maritime views from this 1970s house were not always available.

The owners had lived inland and, having decided to live by the sea, they wanted a better connection with it, so they called in architect Robin Mandal.

“When I arrived there were small windows at the back of the house and very little light,” says Mandal, who wrapped a glassy extension along the rear and around to the side of the house where it met a former garage to create a separate apartment.

The concrete frame extension is supported on 40ft deep piles and plays a supportive role for the existing house, “which had started to slide into the sea”, says Mandal.

A conservatory on the sea side of the apartment was designed to nurture plants but it’s now turned into a playroom for smaller relatives who visit.

Beside this is a glass-walled seating area to the back of the main house, sitting beneath the main livingroom.

“I could stay here all day,” says Mandal reflecting what must be the sentiments of many. The sea offers both calm and action: in my time here birds, boats and a frogman sailed by.

The chequered expanse of windows here are slanted, forming a point towards the sea. This pointed design is reflected in the bedroom above (in which the en suite is simply sectioned off by a large screen).

The reason for the diagonals is because the view from the road is listed – you must not see anything of the backs of the houses – and this design sucks the additions in from sight. Yet views within the house have been expanded and the lengthened vistas start at the front door where previously you were met by a wall.

One of the residents, Joan McLaughlin, jokes that this is a five-storey house, but these floors flow down the site as half-levels – Mandal has much such hill work in his portfolio – with the kitchen at front door level, the livingroom down some steps from here and the seaside room down again, viewed through two large openings in the former back wall of the house.

The sea room is below the livingroom to bring it closer to the briny and also to create a space to sit in without being easily observed from the room above.

Return stairs up from one bedroom to another have had a hole put in the side wall to bring in light from a kitchen rooflight.

Gathering light from the south and west sides is important in such sites, says Mandal.

“It’s that east coast thing where the view is the opposite way to the sun so you need to get the sun in too,” which he has done in the kitchen.

But then the back room and terraces get the morning sun and you can just imagine solar-powered breakfasts on the quarry-tiled terrace looking out to Dalkey island and beyond. Morning swims are the norm from this house.

The terrace railings are in stainless steel whose condition shows that, beside oceans, the word “stainless” becomes an ambition: it is flecked with brown spots (that could probably be scrubbed off).

Yet part of sea life is accepting the salt-buffing and while the Rationel windows have stood up well, their original yellow has been worn to a warm brown.

While the clients have been happy with the house, Mandal says that if he were to revisit the design, he would now have large expanses of glass, instead of dividing it into panes: but then, glass technology has improved in the 17 years since this house was extended and reconfigured (the livingroom ceiling was raised as part of the work).

Getting planning permission for the extension was “a nightmare, horrendous” but the struggle through planning appeals was worth it.

“I’m absolutely happy with how it turned out,” says McLaughlin. “One of the first things I asked Robin was, ‘can you get me a view of Howth?’ I got that and a Martello tower too.”