What is a gable end?

Within roof framing, a gable end, or gable wall, is a vertical wall that reaches upwards towards the apex of the roof continuing on from the structural walls of the floor below. In UK construction, gable walls are typically constructed from masonry, and continue from the cavity masonry below. This being said, gable ends constructed from timber can be found in modern loft conversion, as well as timber framed houses. The gable end is used as a more space efficient alternative to the hip end. In a pitched roof, the usable space within a hip end is limited by the pitch of the roof, with a large portion of the lower slope being ineffective for storage or living purposes. On the other hand, a gable end increases the usable space within the roof by continuing the height at the apex of the roof all the way to the external walls of the building. Whilst this is a more desirable feature in terms of usable space, more materials are required for the construction of a gable end in comparison to a hip end. There are many varieties of gable end, most of which we’ll look at in more detail later. For now, we’ll look at the most simple - the full height gable.  

For masonry gables, the gable wall is built up to the height of the roof, following the exact pitch of the roof to allow for the effective installation of the roof covering. For a flush gable with no overhang, the masonry extends all the way to the top of the rafters in order to support the ends of the roof covering system. For tiles that are installed with a cement verge, the masonry is laid neatly up to the top of the rafters, with the cement board verge sitting on top of the external skin of the masonry. The roof battens sail over the cavity masonry and pin down the verge board, stopping short of the end so that they can be mucked in with mortar. The tiles are then installed over the battens, and the cement verge is installed.  

This arrangement is also applicable for slate roofs, with the masonry meeting the top of the rafters. The battens extend over the cavity to the edge of the external skin, and are capped with a special slate roof trim - covering the battens from below and providing a weatherproof seal to the top edge of the slates.

What is a barge ladder?

Alternatively, a gable ladder may be installed to create an overhang onto which soffit and fascia can be effectively installed. This arrangement is more decorative, but also provides some additional protection against the elements to the very top of the masonry - a potential weak point in the weathering system. The gable ladder is composed of 2 rafters that are supported by timbers that span through the cavity masonry and are fixed to the end pair of rafters inside the roof structure. The “ladder” is assembled on the floor and lifted into place, supported by the ridge that is sailed long over the masonry. The plates may also be left long temporarily to support the bottom of the ladder during the construction process. Once the ladder is installed, the masonry gable is built up to meet it, with additional masonry being installed between and around the “rungs” of the ladder. When dry, this masonry supports the ladder in its final place.   

What are the criteria of a barge ladder?

The barge ladder must be an appropriate width to receive the correct width of fascia - this is affected by the type of roof covering system that is installed. The ladder must project evenly away from the gable wall at an appropriate width for the soffit. The ladder must be properly supported until the masonry is erected to permanently support it. Failure to correctly support the ladder can lead to a discrepancy in the desired shape of the roof. 

How are barge ladders installed?

The creation and installation of a gable ladder is relatively straightforward, though attention must be paid to the correct installation procedure to achieve the desired outcome. The first step to the successful installation of a gable ladder begins at the beginning of the roof assembly process. Provisions must be made early on to aid in the installation, namely ensuring that the ridge beam and the wall plates extend an appropriate amount beyond the masonry to support the ladder before the masonry is built up to it. The extension of the plates is not strictly necessary as they are cut away after the fact, but they certainly aid in keeping the ladder aligned with the plane of the roof during assembly and installation.  

With the end joist installed on the plates, the end pair of rafters can be situated in place. It's important that these rafters are only temporarily fixed at this stage to allow the ladder assembly to be moved later on if required. Discrepancies in the length of the sides of the building, as well as in the width of the cavity masonry can cause the on centre layout of the rafters and joists to not be parallel with the external skin of the masonry. By temporarily fixing the end pair of rafters, we can move them once the ladder is installed to parallel the ladder with the external skin. The portion of the ridge that projects past the external skin must also be ripped down to width if necessary to ensure it doesn't project below the bottom of the ladder - potentially disrupting the installation of the plastic soffit and fascia capping. 

With these provisions made, we can move onto creating the ladder. The barge timber itself is cut from the pattern rafter, with or without the birdsmouth depending on whether or not we left the wall plates long on the roof. We require two of these rafters, one for each side of the roof. With these timbers prepared, we can measure the desired length of the timber ladder “rungs”. These timbers fix on the inside of the barge timber, and connect to the outside edge of the last pair of rafters. At this stage of the roof framing, the outside course of masonry will be lower than the inside course that supports the wall plate, to allow for the rafter tails to sail freely past the external skin. As such, we must use a spirit level to plumb up from this low outside course to establish the distance from the outside of the last rafter to the outside of the external skin. If the plates are sailed long on the roof, this can be easily marked on the timber. Our timber rungs need to be cut to this length, plus the desired length of the overhang, minus the thickness of the barge timber.  

In this instance, the distance from the last rafter to the outside of the masonry is 397mm (47mm for the joist, 50mm ventilation gap, and 300mm cavity). Our desired soffit overhang is 200mm. If we subtract the thickness of the barge timber, assuming it's a common 2” timber, we are left with an overhang length of 153mm (200mm - 47mm) past the external masonry. Totalled up, the length of our ladder rungs must be 550m (397+153) in order to achieve the desired overall 200mm soffit width.  

To calculate the number of rungs that we need to cut, we must mark out the barge timbers. The first timber rung is installed at the top of the barge timber, perpendicular to the barge timber and as close to the short point of the plumb cut as possible - with a few mm tolerance for a good fit. From this point, 400mm centres are marked out down the length of the barge timber. Timbers that land close to the birdsmouth notch are discounted, as they are interrupted by the joist that sits on the outside of the rafter. The timbers only need to reach the plate anyway, as the very end of the barge ladder is supported by the timber fascia backer until the masonry is installed. These markings should be transferred across both barge timbers, typically across the top edge of the timber so that it can be easily seen when assembling the ladder. Tally up the amount of timbers required and cut them all ready for assembly.  

With all of the timbers cut, we’re ready to assemble the ladder. A nail gun can be helpful to position the timbers into place, though they should be fixed again after the fact with 4” nails. On a flat surface, stand two of the timbers upright at a good distance apart. Carefully place the timber barge on top of these timbers. Being gentle so as not to tip the barge over, locate one of the timbers under one of the layout marks, visually aligning it by looking down the timber. For a good roof installation, we want to ensure that the top of the rungs and the top of the barge timber are flush with each other. With the first timber in place, use the nail gun to temporarily pin it in place. Going to the other end of the barge, we can repeat this process. Care should be taken to ensure that all of the rungs are installed perpendicular to the barge timber. The ladder will now stand self supported on the flat surface. We can then go along the timber from one end, lifting it slightly to slide the rungs into place and fixing them in position with the nail gun. With all the timbers in place, we can go back along the barge and place 2-3 4” nails through the barge and into the rungs. With one ladder completed, the other can be assembled. Take care here to ensure that the second ladder is assembled in the correct opposite orientation to the first ladder. 

Once the ladders are assembled, we’re ready to fix them to the existing roof structure. Regardless of the size of the ladder, all of the additional timber used to create it makes these components relatively heavy. As such, it’s important to prop the plate up to the correct height off of the scaffold if it is left long before the ladder is installed, else the weight will bow it downwards. Bracing may also be required between the two plates to prevent them from spreading apart under the weight of the ladder. Using another operative if required, the ladder can be lifted into place against the existing structure. The plumb cut of the barge ladder will meet the extended ridge as required, with the rungs coming tight against the last rafter. A temporary fixing is placed through the top of the rafter into the ridge to hold it in place, with another fixing being installed through the last rafter into the bottom rung. This process is repeated on both sides so that the ladder is located approximately in place. Some more temporary fixings are placed through the last rafter into the rungs to ensure that the ladder is up tight against the last pair of rafters.  

Once this is achieved, we can perform our checks to ensure that the ladder is in the correct location before fixing it up. The first check is to ensure that the distance from the external skin to the outside edge of the barge timber is identical on both sides. A tolerance of a few mm is allowable here. Any more than this, and we must undo the temporary fixings in the last rafter and slide it backwards until the measurements are the same. With the bottom location of the barge correct, we can check it for plumb. Pull a string line between the two correct bottoms of the barge at the height of the wall plates. A plumb bob or spirit level should intersect this line perfectly, again with a few mm tolerance. Any lateral adjustments can be made by unscrewing the top fixings of the barge and the last rafter and sliding the assembly backwards or forwards until the outside edge of the barge is directly above the line pulled between the two bottoms. 

Once this is achieved, the barge is located correctly and ready to be fully fixed. Permanent fixings can be installed in the bottom and tops of the rafters. The timber rungs can be nailed to the last rafter pair with 4” nails, using a square to ensure that they are perpendicular between the two rafters. Timber props can then be screwed to the outside of the barge off of the scaffold to hold it at the correct height whilst the masonry is built up around it. With the props in place, the excess wall plate can be removed if required, as this will disrupt the installation of the plastic capping. A final check can be made to ensure that the ladder hasn't dropped below the plane of the roof by holding a straight edge across the top of the rafters. The top is supported by the long ridge, and so this is very unlikely to have sagged. Sagging in the ladder typically occurs towards the lower half of the roof. If it is sagging, timber can be screwed across the tops of the rafters and into the barge to pull it back up to height. The props can then be adjusted to stabilise it in place. Any additional ridge that projects past the barge can then be cut off flush with the barge.  

How are gable restraint straps installed?

Regardless of the particular construction of a masonry gable end, gable restraint straps must be installed. Due to the large flat surface of the roof in close proximity to the large surface area of the gable end, high winds can create extreme pockets of negative pressure at the termination of the roof on gable ends, as demonstrated by Bernoulli's principle. If not adequately retained, this negative pressure can easily pull the masonry outwards away from the building, creating a very serious hazard to those in close proximity. In order to retain this large area of masonry, gable restraint straps are installed as a part of the roof structure in order to tie the two components together. Whilst a gable ladder does provide some stability to a masonry gable end through its rungs, gable restraint straps are a mandated component as specified by the NHBC standards “7.2.8 - restraint”. These straps are installed on the top side of the joists and the underside of the rafters, projecting through the inside skin of the masonry and tying the structure to the roof assembly. As per usual, the external skin of the masonry is tied to the internal skin through the use of cavity wall ties.  

For the joists, 3-4 straps are installed depending on the span of the roof. In a loft space, these straps are installed directly over the joists. In a loft conversion scenario, the straps are slightly let into the top of the joists to prevent interruptions to the floor boards. To ensure that these straps are installed by the bricklayers, we carpenters lay them in place and temporarily secure them with bent over nails. This allows the bricklayers to slide them in and out to suit their masonry, whilst ensuring that they are not accidentally left out. As the inside skin is erected, these straps are pulled forwards and hooked over the inside of the blocks. Once they are in place, we can nail them into the joists. Supporting timber blocking must be installed underneath the straps between any joists that support the straps.  

For the rafters, 2-3 straps must be used at equal points up the roofs, fixed to the underside of the rafters. These straps need not be let into the rafters in any scenario. The same method of temporary fixing is used to allow the bricklayers to move the strap in and out to the desired location. Once installed, blocking is installed as usual to support the straps.