Who this guide is for
- Owners adding anything to an external wall, a roof or an insulated lining
- Readers who have been told not to drill into a wall and want to know why
- Facilities and maintenance staff mounting equipment on a finished building
- Renovators fixing into walls whose build-up they did not install
- Anyone preparing questions before a bracket, screen or plant item is installed
What the fixing reaches is rarely what it appears to reach
On a hung, screened or faced envelope, the visible surface is not the structure and is frequently not able to carry anything besides itself. The rainscreen record states that fixing anything back to cladding panels rather than to a nominated backing element loads a component that was designed only to carry itself. The shading record makes the same point from the other side: identifying the structural component the element is genuinely fixed to is a design act, because the visible facade in front of it is usually incapable of the duty.
A brick slip facade shows the trap most clearly. The record describes a facade that reads as brickwork from the street while contributing no bearing of its own, and notes that fixing anything into it later, from a light to a handrail, means fixing into a carrier rather than into a wall. Appearance is described there as not evidence of construction.
- A masonry face can be a self-supporting leaf, a veneer or a thin facing on a carrier
- A rainscreen panel carries itself and its wind load, and nothing else by default
- A carrier rail, board or panel is what a slip facade actually hangs from
- The backing element that can take a load is identified rather than assumed
Loading a member that was designed for wind
Some elements are structural but not for the load you are about to apply. The curtain walling record notes that fixing anything to a mullion after completion loads a member designed for wind and may cross the isolating component within its section. The shading record describes fins and louvres frequently fixed directly to facade frames, which asks a member designed for wind to carry a cantilever as well.
The distinction the records draw is between weight and leverage. A cantilevered element multiplies its own weight into leverage at the fixing, and wind on a projecting element both pushes and lifts rather than simply pressing. Whether a given member can accept that is a structural matter, and the records place it with the facade engineer rather than with the person making the fixing.
Punctures that leave no visible sign
Where a lining carries a control layer, an ordinary fixing is a hole in it. The internal insulation record is direct: fixing shelves, rails or cabinets through a completed lining can puncture the control layer without any visible sign that it has happened, and a finished insulated lining is indistinguishable from an ordinary wall. It also notes that later work chasing into the lining will reach the sealed layer if the service zone was omitted, and that the damage will not be visible.
The same applies outboard. A bracket crossing a rainscreen passes through the insulation and usually through the control layer as well, so load is transferred, a path is created around the insulation and the sheet is perforated at one point. The penetration record adds that sealing only the outer panel makes the detail look finished while the plane behind it stays open.
Fixings that cross a waterproofing layer
On a roof the layer being crossed is the one keeping water out, and in most of the assemblies described it is concealed. The trafficked deck record notes that every post, planter fixing, screen or mounted item transfers load down through the build-up, and that these are penetrations of the water-resisting layer made at the roof edge, which is the place with the least tolerance for one. It also states that fixing anything into a completed terrace, including a planter, screen or light, may penetrate a concealed water-resisting layer.
The plinth interface describes what happens when the termination around an isolated object ends up below the water it was meant to stand above: the roof's weather line stops underwater at a position concealed beneath the plant, water appears in the room below commonly nowhere near the plinth, and establishing why means disconnecting or lifting equipment before the layer can be looked at.
- An upstand exists to raise a termination above the water crossing the roof
- A plinth puts that termination in the field, with water running past on every side
- Guarding and screen anchorages land at the perimeter, where the layer is already turning up
- A fixing near an outlet meets water that has already been gathered
Removing the freedom something relied on
The least obvious consequence is that a fixing can stop something moving. The precast record states that adding fixings to a hung panel to make it feel more secure can remove the freedom the design relied on to absorb structural movement, and describes a panel held rigidly at more than one bearing point as receiving the structure's shortening and deflection instead of accommodating them. The curtain walling record describes a restraint that locks rather than slides as bringing the weight of the framing above to bear on the frame beneath it.
Seamed metal behaves the same way. Its record notes that any detail that grips the tray away from its anchor becomes a second anchor whether or not it was drawn as one, and that a tray anchored at each end, or restrained accidentally by a badly formed detail, has nowhere to put its expansion. A fixing that feels reassuringly solid is exactly the one that has done this.
Fewer, planned crossings rather than better-sealed ones
The recurring answer in the records is not a better seal but fewer holes. The penetration record puts it plainly: a penetration never made needs no seal, no return and no collar, and where services are distributed in a zone inboard of the control layers, the barriers are crossed at planned points instead of wherever a fixing or bracket happened to land. Grouping penetrations, and forming them before a roof is covered rather than after, is described as materially easier than working back down through a completed build-up.
It also matters that the crossing is made rather than filled. The sleeve gives the building a clean, stable edge a bond can hold to, and the seal closes the remaining annulus around an object that will not stay still; sealant applied straight into a rough perforation is described as being asked to be both at once, and letting go at whichever edge moves first.
What to establish before the drill comes out
The practical sequence in the records is to find out what the element is, what the fixing has to reach, what it will cross on the way, and who is responsible for the consequence. Each of the facade records offers a physical test for identifying the construction, and the internal insulation record asks directly what an owner should do differently when hanging or fixing anything on those walls afterwards.
Where there is a record of the build-up, this is what it is for. Where there is not, the records are consistent that the position of concealed layers cannot be deduced from the finished surface, which makes the question one for whoever designed or installed the envelope rather than one to be settled by looking.
Questions before fixing anything to a finished envelope
- 1Establish what the visible surface actually is before treating it as a wall
- 2Ask which element the fixing is intended to reach, and how it will be found
- 3Ask whether that element was chosen and checked to receive this load
- 4Establish whether the item cantilevers, and whether wind will lift as well as push
- 5List every layer the fixing will cross between the surface and its anchorage
- 6Ask whether a concealed control layer runs behind this surface
- 7On a roof, establish where the water-resisting layer sits and how it is protected
- 8Ask whether the fixing position sits in the path water takes across the surface
- 9Check whether the element being fixed to was designed to move
- 10Ask whether the crossing can be grouped with others rather than made on its own
- 11Ask what forms the edge of the hole, and what closes the gap around what passes through
- 12Establish how the crossing could later be opened and remade without cutting the plane
- 13Check whether any record of the build-up exists before assuming there is none
- 14Agree who is responsible for the crossing, as distinct from the item and the wall
Common mistakes to avoid
- Treating a cladding panel, a slip or a carrier board as a wall
- Fixing to a mullion or rail because it feels solid rather than because it was checked
- Adding a fixing to a hung panel to make it feel more secure
- Drilling into an insulated lining as though it were an ordinary plastered wall
- Sealing at the visible outer face and leaving the plane behind it open
- Founding a roof fixing where water is already concentrated or where it will pond
- Relying on sealant alone in a rough hole around something that moves
- Making crossings one at a time as each item arrives, rather than planning them
When to involve a professional
- Ask which structural element each fixing reaches and whether it was checked for this load
- Ask how the penetration through cladding, insulation and control layers is sealed
- Ask whether an isolating component is needed where a bracket links outside to inside
- Ask, on a roof, how the water-resisting layer is returned around the fixing
- Ask whether the element being fixed to was relied on to move, and what the fixing does to that
- Agree who records the crossing so that later work knows it is there
Frequently asked questions
Questions readers ask about this topic
Can I fix a light or a handrail to a brick-faced wall?
It depends on what the brick face is. The records describe three constructions that look alike from the pavement: a self-supporting leaf on a bearing, a veneer anchored back to a frame, and thin facings on a carrier with no bearing of their own. In the last case a fixing reaches a carrier rather than a wall, which the record says needs checking first.
How would I know there is a control layer behind my lining?
Usually you would not by looking. The internal insulation record states that a finished insulated lining is indistinguishable from an ordinary wall, and that a fixing can puncture the layer with no visible sign. It treats a drawing of what was installed, and where fixings may safely be made, as part of the assembly rather than paperwork about it.
Is a roof fixing safer if it is well sealed?
Sealing is only part of it. The records describe a penetration as needing a defined edge, a seal that tolerates movement, and a separate return to each plane crossed, and note that a perforation on a horizontal surface is a joint in the plane most likely to hold water. Where the fixing sits relative to falls and outlets changes what the seal is being asked to resist.
Why would adding a fixing make something worse?
Because some elements are held deliberately loosely. The records describe hung panels restrained at points that must be free to slide, curtain walling frames whose restraints must not lock, and seamed metal trays anchored at one position so the rest can travel. An extra fixing in any of those becomes a second anchor, and the movement it prevented has to go somewhere.
What is the alternative to making the fixing?
The records favour fewer and earlier crossings rather than better ones. Grouping penetrations, planning them before a build-up is closed, and running services in a zone inboard of the control layers are all described as reducing the number of crossings, and a penetration never made is noted as needing no seal, no return and no collar at all.
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