Do you want to add a new opening to your house? New back door, access to the utility, a room with a view – whatever the reason we look at what you need to consider and whether you can do it yourself.

We as architects are often asked about knocking through an internal or external wall. Is it feasible, are the walls load bearing, how much will it cost? Whether to connect an existing room to an extension, opening up two rooms into one or making a new opening in an external wall to bring more light and aspect into a room, there are many things to consider before starting.

It is possible to knock through most walls; the first step therefore shouldn’t be about whether it is. As with all good design you should think the project through – in this case consider if you have chosen the right location to knock through. What impact will this opening have on existing and future layouts of furniture within both rooms, what door type is most appropriate e.g. standard or glazed door, sliding door, pocket or concertina door, and are the two spaces that you are knocking through really best suited to each other in use, e.g. bedroom located off a kitchen, bathroom located off a living space, etc. 

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Staying on the topic of internal openings, the work is often carried out to remedy a layout that currently does not suit the homeowner’s way of life. The typical scenario of opening up an existing living space to an underused dining room should provide guidance as this can often lead to losing points of ingress, e.g. closing off the existing access from the hallway to retain wall space. 

Apart from the potential inconvenience know that if you create an ‘inner room’, that is, one that is accessed through another and not directly connected to the hallway (unless a utility room or bathroom), and you have added doors within the internal opening, then you will most likely have to provide a fire escape window or door from that inner room to the outside, to satisfy current building regulations in NI and ROI.Also make sure you do not place the opening too close to the corner of the room. Apart from structural issues, you will not be able to install full width architraves and skirting boards to all sides of the doorway, and nothing looks worse! 

With an external opening, the common scenario is that it is desired because the house relates poorly to the outside or that existing windows are too small and do not make the most of their aspect. Before you widen the openings or make new ones, consider a few points: you may gain a view but will that mean you lose wall space for furniture? What will you see from the window or door and at what height should it be set?

For example, if it is a new window within a lounge you will want to be able to look out of it while seated. If it is a panoramic or feature window, think about how you are going to break it up as this has a significant bearing on the cost, i.e. one large pane of glass, positioning and height of opening windows, impact of crossbars, (mullions and transoms) on your view.

Planning Permission and Building Control

Unless you live in a listed building, you do not require planning permission to create new doorways or windows internally. Similarly, small or singular external openings often do not either if they are to the rear or side of the property, but as every house is different and has differing relationships to boundaries, proximity to neighbours etc., the best advice is to contact your local planning department and query it with them directly. Larger openings or openings to the front elevation should always be discussed with an architect or your local planning department.

In NI you always require building control approval to create new window and door openings. Depending on their size, the department may request a structural calculation or certification for the lintel or steel beam over. This generally is only if beyond a standard 1-2m opening. A way around this is to use an approved off-the-shelf lintel from a supplier who can provide you with a calculation for building control. Always confirm the support you are using with building control in advance of carrying out any work. 

In ROI you do not currently require building control approval to create a new internal opening within a dwelling. For an external opening it will be if a planning application is involved and this entails notifying the local authority with a commencement notice (without documentation). However the onus is always on the home owner and builder to conform to current building control standards. 

If the opening is larger than 2m, then it is always recommended to involve a structural engineer regardless of location. A design professional, or in the case of NI, building control, will also consider what knock-on effects might result from your actions, e.g. the fire escape may have been compromised by inadvertently blocking it up. 


With the aid of steel and concrete lintels, most walls can be opened up without much issue. A lintel is a load bearing support that spans the width of the opening to support the weight above. On standard single and double door openings, this is typically achieved using a pre-stressed concrete lintel, which is relatively inexpensive, but make sure there are at least three courses of blockwork over it as this gives the concrete lintels added strength. 

Once you exceed the standard widths for concrete lintels e.g. typically over 2.5-2.8m, then you will require a steel lintel over the opening to span the greater distance, e.g. a proprietary insulated lintel or standard sized steel beam from your local steelwork supplier. Steelwork lintels are typically more expensive and require 100mm reinforced concrete load bearing pads, 250mm minimum under the steel beams. 

The big question for both windows and doors is how to tell what is and isn’t load bearing. You may think that if the wall is timber studwork it’s non load-bearing, but that’s not true! In many older properties, some of the internal studwork walls could be carrying load either from floor joists above or from the roof. New build timber frame homes can also have load bearing internal and external timber framed walls.

A good rule of thumb is to follow the wall from the ground up to see where it goes and what lies above it. Follow it into the floor space and see if it lines up with walls above that might take support from it below. Also look in the roof space and see if it stops at the ceiling joist level or whether it carries on up to support heavy roof timbers or rafters. Also have a look at the floor covering, if it’s timber the joists are going the opposite way. If in any doubt, seek professional guidance from an architect, structural engineer or contractor.