9 minute read
Office refurbishments
Office refurbishments
Kelly Harrison discusses how engineered timber offers solutions to the challenges of adapting existing buildings, and highlights lessons learned. Glulam column baseplate on RC slab CLT wall on load-bearing masonry
With climate targets and deadlines closing in, adapting and retrofitting buildings is a brilliant way of achieving low-impact developments. But how can this be achieved if the existing building does not have the required layout, enough net floor area or is generally an unknown?
The fact is, existing buildings often have built-in excess capacity. With thorough research to find the original drawings and investigations to expose and test structure on site, it is possible to adapt and extend to suit a new market, rather than demolish and start again.
Refurbishment brings challenges:
• Strengthening existing foundations is difficult and costly. • Existing superstructure may not be laid out in an optimum arrangement. • The buildability in and around an existing building and site, especially when some areas are occupied, can create logistical and viability issues.
Raise your Glulam 150mm if on a slab on ground!
Steel plate and dowels to take any tie forces - plugged for fire protection
Resin anchors into RC slab - glulam notched around steel plate
Glulam column baseplate on RC slab Glulam column baseplate on reinforced concrete slab. Drawing: Kelly Harrison CLT wall on load-bearing masonry Glulam beam connection to side of RC slab
Holes cut in plate, and flood welded Tolerance and chamfers around fin plate considered in design!
Rivets to be surveyed!
Glulam column baseplate on steel beam. Drawing: Kelly Harrison
Glulam column baseplate on steel beam
Engineered timber has solutions to many of these issues. Its high strength-to-weight ratio means that it has the capacity to support the required loads while adding much less weight to the existing structure and its foundations than other materials. Strengthening and work in the ground are therefore significantly reduced. Its off-site factory production, and minimal weight, are also ideal if you need the surrounding existing building to remain in use during construction, or if CLT bolted there is any below-ground infrastructure such as rail tunnels through steel or services – the use of engineered timber can help reduce shoe plate, anchored to the programme time and minimise risk and disruption. concrete padstone
Older buildings usually have a smaller grid than new-build offices and these grids are often ideal for timber. Crosslaminated timber (CLT) floors require a certain thickness for Think about fire and acoustic reasons, so why not make that thickness access with this connection! Can work at capacity, not wasting any material, rather than both sides be adding thick acoustic build-ups and other heavy materials reached safely? to achieve this afterwards? CLT can often span further than standard office secondary grids, which in turn reduces the amount of beams in the soffit and often then tying in well with an existing 4.5m or 7.5m column grid. >>
CLT bolted through steel shoe plate, anchored to concrete padstone Everything must be surveyed, at various stages – early, post-strip out, post-demolition – and as the design develops, a rolling programme of investigations and site measures Survey!! is required. Existing structures will not only have different Existing slab tolerances but may also have moved over time, and edge Bearing plate anchored toengineered timber is precise. The design team should top face of RC consider this from the early stages to take out any differences slab - scan for between the two materials and ensure the extension is rebar. buildable and aesthetically pleasing. Standard panel sizes should also be considered within the parameters of the existing structure; how can minimal waste and the positions of joints work with the aesthetic of the existing space?
Raise your Glulam 150mm if on a slab on ground!
Steel plate and dowels to take any tie forces - plugged for fire protection Think about access with this connection! Can both sides be reached safely?
CLT wall onCLT wall on loadbearing masonry. Drawing: Kelly Harrison Resin anchors intoload-bearing masonryRC slab - glulam notched around The design steel plate Survey!! Designers must be mindful of the connections they are Existing slabPlate andStrengthening Recommended if proposing to the existing structure from the start of the edgedowels to resist tie screws to prevent connecting to a thin slab edge - for anchor edgeprocess. Connections should be designed early on by the forcessplitting distance and capacity. consultants, or with early input from the fabricators, to ensure that the architect and client understand the aesthetic nature of CLT bolted through steel the connections and the sub-contractor can investigate their shoe plate, buildability at pricing stage. anchored to concrete padstone Glulam beam connection Considerationsto side of RC slab
Strengthening Plate andExisting buildings may have low floor-to-floor zones so careful screws toThink about dowels to consideration of the grid and therefore member depth, along preventaccess with this...Perhaps a better resist tie with the building services solution, is required when extending Existing buildings come in all shapes and sizes, and different splittingconnection! Can both sides beTolerance and detail if access only possible on one side forces engineered timber products can suit various constructions. chamfers laterally. The timber may not be placed at the same level as reached safely? around fin the existing adjacent slab for the best solution, but how will Think about the that appear visually and is there a good detail to address the junction of the two? >> Reinforced concrete buildings often have built-in excess capacity and are relatively simple to extend, but internal alterations are often more difficult due to the monolithic nature of the slabs. Timber frame, with glued laminated Glulam column baseplate on RC slab CLT wall on load-bearing masonry Glulam beam connection to side of RC slab plate considered in design! What are the tolerances between these materials? CLT - precise! reinforcement you cannot see. Rivets to be timber (glulam) or laminated veneer lumber (LVL) beams and columns, can be anchored into the existing structure. RC padstone - large tolerance allowance surveyed! ...Perhaps a better Plate can be over-sized with detail if access only more holes than With an existing steel building it is very simple to extend with a hybrid steel and CLT solution. This can also work Tolerance and chamfers around fin Existing wall - potentially out of plum possible on one side required, and the worst case combination of well with a glulam frame, as the baseplates and connecting plates are often also made from steel. If the building plate considered in design! Design your connection for the worst scenario! What are the tolerances between these materials? anchors considered in calculation. dates from the first part of the 20th Century it may have CLT - precise! Holes cut in rivets on the existing beams and columns, which should Rivets to be plate, and be surveyed prior to detailing and production of the surveyed! RC padstone - large toleranceflood welded connections. Steel frames don’t always have the excess allowance capacity required, but are much easier to strengthen using CLT wall on load-bearing Glulam beam to RC new steel plates and members. masonry - alternative Existing wall - potentially out of column plum CLT walls can be used to extend masonry wall structures in the same form, but with a more lightweight material. The connection between the two walls, whether on top or to the side, should be given due consideration, not only in terms of transferring loads but also with regard to aesthetics, access (if a party or external wall) and, not least, fire and acoustic requirements.
Design your connection for the worst scenario!
Survey!! Existing slab edge Bearing plate anchored to top face of RC slab - scan for rebar.
Strengthening screws to prevent splitting
Bearing plate anchored to top face of RC slab - scan for rebar.Plate and dowels to resist tie forces Recommended if connecting to a thin slab edge - for anchor edge distance and capacity.
Glulam beam connection to side of reinforced concrete slab. Drawing: Kelly Harrison Acoustic separation is a challenge with CLT; its lightweight nature means that it has little mass to stop noise transfer. This must be addressed early on, as the acoustic build-up can add to the floor thickness and therefore increase the floor-to-floor height of the building. In some situations it can also cancel out the weight saving gained by using CLT in the first place, and detrimentally increase the strengthening required to the existing structure below. Products and details are available that provide a relatively heavy finish over a raised floor, which can increase the performance. There are no building regulations for acoustic separation between office floors and so clients should understand what they are requesting and its impact on the carbon footprint of the building.
Strengthening Plate and Recommended if When extending any building laterally or vertically the fire rating and performance of the structure will need to be dowels to resist tie forces screws to prevent splitting connecting to a thin slab edge - for anchor edge distance and capacity. Glulam beam connection to side of RC slab addressed. A fire risk assessment may be appropriate to ensure that the extension does not create a higher risk than in the original building. Timber is a combustible material and ...Perhaps a better detail if access only therefore a self-extinguishment analysis by a fire engineer possible on one side may be the best approach to obtain an appropriate fire Glulam beam connection to side of RC slab design period, along with agreement of details between compartments and at junctions with the existing structure.What are the tolerances between these materials?
CLT - precise!
RC padstone - large tolerance allowance
Existing wall - potentially out of plum
Design your connection for the worst scenario!
Design your connection for the
CLT wall on load-bearing masonry - alternative
Think about the reinforcement you cannot see.
Plate can be over-sized with more holes than required, and the worst case combination of anchors considered in calculation. Glulam beam to RC column Waterproofing details, temporary for the build and proposed for the design, should be considered carefully. If the existing building is occupied at lower floor levels or in part, a temporary roof may be appropriate. A detailed water management plan should be provided by the main contractor to manage the water by all trades until the building is completely watertight. A temporary watershedding and drainage solution must be in place during Think about the construction which ensures that water is routed away from reinforcement areas that may be susceptible to ponding or other surface you cannot see. wetting so there is no water damage to the timber. Water damage must be prevented at joints, for example by taping over and sealing them in such a way as to ensure no leakage into the centre of a member or panel, and that colour Plate can be changes develop evenly over time across the surface. over-sized with more holes than required, and the Summaryworst case combination of Retrofit with engineered timber is the future, but the anchors considered in design team must be willing to survey and develop details calculation. as they go. n
About the author
Kelly Harrison Associate Director Whitby Wood TRADA Board Member
