Could wooden buildings be a solution to climate change?
人类建筑的未来趋势：采用木质建材对抗气候暖化

I’m standing in a seemingly ordinary construction site of an unremarkable office block in east London. The seven-storey building is about two-thirds complete – the basic structure and staircases are in place, with plastering and wiring just beginning. But as I walk around, something different slowly reveals itself. The construction site is quiet and clean – it even smells good. And there’s an awful lot of wood. Building sites typically feature wood as the mould to pour the concrete into. But here, the wood is the concrete.

这是东伦敦一个看来普通不过的办公楼建筑工地。七层高的楼房已建成了三分之二，基本结构和楼梯部分已经各就各位，正在开始为墙壁抹灰泥和铺设管道线路。待我东张西望到处走动，才慢慢发现这座未完工的大楼有非同寻常之处。建筑工地安静而又干净，甚至还有一股好闻的气味。工地上堆着大量的木材。建筑工地通常以木材作框以浇筑混凝土。但在这个工地上，木材充当的就是混凝土的功能。

“Because a timber building weighs 20% of a concrete building, the gravitational load is vastly reduced,” enthuses Andrew Waugh, the architect, who shows me around. “That means we need minimal foundations, we don’t need massive amounts of concrete in the ground. We have a timber core, timber walls and timber floor slabs – so we reduce the amount of steel down to a bare minimum.” Steel is typically used to form the main internal supports or to reinforce concrete in most large modern buildings. In this wooden building, however, there are relatively few steel sections. Those that remain are bolted together like a Meccano set, to be easily taken apart at the end of (or during) the building’s life. “If you wanted to put a staircase right here,” says Waugh, pointing to the ceiling, “you unscrew that [steel] beam there, get a chainsaw and cut a hole in the timber [floor].”

领着我参观的建筑师安德鲁‧沃（Andrew Waugh）兴奋地告诉我，“木结构建筑的重量只有混凝土建筑的20%，因此大楼的重力负荷大幅减轻。这就是说，我们只需要最基本的地基就可以了，不需要浇筑庞大的混凝土地基。我们以木材作建筑主结构，再加上木墙和木地板，因此可以把钢材的数量减少到最低限度。”大多数大型现代建筑通常用钢材做主要的承重梁柱，并用钢筋或钢骨来强化混凝土的拉力。然而这座木结构楼房只使用了很少的钢材。而这些钢材如同英国麦卡诺（Meccano）品牌的模型组合玩具一样是用螺栓固定在一起，在楼房的使用寿命结束时或使用期间要拆开都很容易。沃指着天花板说，“要是你想在这里加建一个楼梯，你只需要拧开钢梁的螺丝，拿把链锯，在木地板上锯个洞就能办到。”

Our dependency on concrete and steel to build everything from homes to sports stadiums, comes at a severe environmental cost. Concrete is responsible for 4-8% of the world’s carbon dioxide (CO2) emissions. Second only to water, it is the most widely used substance on Earth, accounting for around 85% of all mining and linked to an alarming depletion of the world’s sand. Globally, enough concrete is poured each year to cover the whole of England.

当代建筑，从住房到体育场馆，完全依赖混凝土和钢材做建材，结果是付出严重的环保代价。混凝土造成的碳排放量占全球二氧化碳排放量的4%至8%。制作混凝土的砂石开采量仅次于地球上使用最广泛的自然资源水，砂石开采量约占全球所有采矿业的85%，结果是造成全球的海沙河沙惊人的枯竭。现在全球每年浇筑的混凝土足以覆盖整个英格兰。

Some architects such as Waugh are therefore arguing for – and pressing ahead with – a return to wood as our primary building material. Wood from managed forestry actually stores carbon as opposed to emitting it: as trees grow, they absorb CO2 from the atmosphere. As a rule of thumb, a cubic metre of wood contains around a tonne of CO2 (more or less, depending on the species of tree) – which is similar to 350 litres of gasoline.

因此，以安德鲁‧沃为代表的一些建筑师主张回归传统，用木材作为今后人类建筑的主材料，并身体力行地推动他们的主张。木材如果是取自于受到人工管理的森林，实际上是有助于碳的储存，而不是将碳排放到大气中，因为树木在生长过程中，会从大气中吸收二氧化碳。根据过往经验，每立方米木材含有大约一吨的二氧化碳，相当于350升汽油。至于实际存储多少，则取决于树木的种类。

Not only does wood remove more CO2 from the atmosphere than it adds through manufacture, but by replacing carbon-intensive materials such as concrete or steel it doubles its contribution to lowering CO2. A recent advisory report to the UK government on the uses of “Biomass in a low-carbon economy” found that, “the greatest levels of [greenhouse gas] abatement from biomass currently occur when wood is used as a construction material… to both store carbon and displace high carbon cement, brick and steel.”

用木料做建材不仅仅因为其从大气中吸收的二氧化碳比其释放的二氧化碳要多，而且因为取代混凝土或钢铁等碳排放量巨大的建筑材料，木材对降低大气中的二氧化碳含量又多了一重贡献。最近一份题为《低碳经济中的生物质能》的咨询报告送交给英国政府。报告指出，“使用木材作建筑材料……既储存碳，又替代高碳排放的水泥、砖和钢铁等材料，因此生物质能可以最高水平减少温室气体。”

Between 15% and 28% of new homes built in the UK annually use timber frame construction, capturing over one million tonnes of CO2 a year as a result. Increasing the use of timber in construction could triple that amount, the report concluded. “Savings of a similar magnitude may also be possible in the commercial and industrial sectors by utilising new engineered wood systems such as cross-laminated timber.”

现在英国每年新落成的房屋，有15%到28%使用的是木结构建筑，因而每年捕获的二氧化碳超过100万吨。该报告的结论是，增加建筑木材量可能使这一数字增加两倍。“在商业和工业部门使用新的工程木料，例如交叉层压木板（CIT），也可能节省同样数量的碳排放。”

Cross-laminated timber, or CLT, is the primary material on the construction site Andrew Waugh shows me around in east London. Because it’s described as an “engineered wood”, I expect to see something similar to chipboard or plywood. But CLT just looks like ordinary 3m (10ft) planks of wood, one inch thick, replete with knot-holes and splinters. The ingenuity is that the planks are made stronger by gluing them in layers of three, with each layer perpendicular to the other. This means that the CLT “doesn’t bow or bend, it has integral strength in two directions”, says Waugh. “[A CLT] wall supports the floor above, with a horizontal strength to carry a load above it, acting like a long beam”. That, he says, “changes architecture”.

安德鲁·沃带我参观的东伦敦建筑工地，其主要材料就是交叉层压木板。因为称之为“工程木料”，我以为看到的会是刨花木板或胶合板之类的东西。实际上，交叉层压木板看起来就像普通的3米，即10英尺长木板，有1英寸厚，板面满布木节孔和木纹。其天才的设计在于，木板是三层粘合而成，每层均与邻层纹路垂直相交，从而十分坚固。安德鲁‧沃表示，这意味着交叉层压木板“不会向上也不会向下弯曲，水平垂直两个方向的强度都很高”。他说，“交叉层压木板墙身能支撑整个上层的地板，其水平向的强度足以承载上层楼的荷载，犹如一根长梁一样”。这“改变了建筑”。

Having built with CLT for a decade now, Waugh believes it can achieve anything a concrete and steel building can, and more besides. It was invented in the 1990s, partly in response to “the death of the furniture and paper industries”, says Waugh. “Sixty percent of Austria is forest and they needed to find a new sales outlet. So, they came up with cross-laminated timber.”

安德鲁·沃使用交叉层压木板建房已经有10年历史，他相信这种木材可以做到任何混凝土和钢铁建筑可以做到的事，甚至更多。他说，交叉层压木板是上世纪90年代发明的，部分原因是为了解决“家具和造纸工业的消亡”。“奥地利60%的土地是森林，他们需要为木材找到一个新的销售渠道门路。所以，奥地利人发明了交叉层压木板这种新的工程木料。”

Other engineered woods such as plywood and MDF are around 10% adhesive (glue), often urea-formaldehyde, which can produce hazardous chemicals during recycling or incineration. CLT, however, is below 1% adhesive, and typically uses a bio-based polyurethane. The planks are bonded together under heat and pressure to fuse that small amount of adhesive using the moisture of the wood. To look at, smell and touch, it’s as pure wood as a child’s tree house – knots and all.

胶合板和中密度纤维板等工程木材，含有10%左右的粘合剂，即所谓胶水，通常是一种叫脲醛的化学物，在回收或焚烧过程中会产生有害化学物质。但交叉层压木板的黏合剂含量则低于1%，通常使用比较环保的生物聚氨酯。木板在高温和压力下粘合在一起，少量的粘合剂则被木材中的湿气所融化。看着这种木板，再用鼻子闻一闻，用手摸一摸，感觉就像为孩子建的树屋一样，是带着木质疤痕和纹路的纯粹木头。

Many CLT factories in Austria are even powered by renewable biomass using the offcuts, branches and twigs. Some factories produce enough electricity to power the surrounding communities.

奥地利许多生产交叉层压木材的工厂为了环保，甚至使用可再生的生物质能来作燃料，如木材边角废料、树皮和树枝等。一些工厂用生物质能生产的电力还足够供应周围的社区。

Despite the fact that CLT was invented in Austria, Waugh’s London-based architecture practice, Waugh Thistleton, was the first to use it to construct a multi-storey building. Murray Grove, an otherwise ordinary nine-floor apartment block with grey cladding, caused “shock and horror in Austria” when it was being built in 2009, says Waugh. CLT had only ever been used for “nice and simple two-storey houses”, whereas anything taller reverted to concrete and steel. But for Murray Grove, the entire structure above the first floor slab is comprised of CLT panels, with all walls, floor slabs and lift cores formed from timber, like a honeycomb block.

尽管交叉层压木材是奥地利发明的，但第一个使用这种建材来建造多层楼房的公司是安德鲁‧沃的伦敦建筑事务所。默里格罗夫大厦（Murray Grove）是伦敦街头一栋普通的九层公寓楼，楼面是灰色的。安德鲁‧沃说，2009年这座大厦落成时，“在奥地利引起了震惊和恐慌”。因为在此之前交叉层压木只用来建造“漂亮而简单的两层楼房子”，而高于两层楼的房子则会恢复到混凝土和钢结构。但是默里格罗夫大厦的一楼以上的整个结构全由交叉层压木板组成，所有的墙壁、楼板和电梯内壁都是这种木板，很像蜂窝块一样。

The project has since inspired hundreds of architects to build tall with CLT, from the 55m Brock Commons Tallwood House, in Vancouver, Canada, to the 84m, 24-storey 'HoHo Tower' currently under construction in Vienna, Austria.

默里格罗夫大厦的成功启发了全球数百名建筑师使用交叉层压木板建造高楼，其中最高的是加拿大温哥华的布洛克卡芒区高55米的高木大楼（ Tallwood House）。奥地利维也纳即将超越这个记录，目前正在建设将高达84米的24层和和高楼（HoHo Tower）。

Recently there have been calls for tree planting on a colossal scale to capture CO2 and curb climate change. However, whilst young trees are efficient and effective carbon sinks, the same is not so true for mature trees. The Earth maintains a balanced carbon cycle – trees (along with all other plants and animals) grow using carbon, they fall and die, and release that carbon again. That balance was knocked out of kilter when humans discovered ancient stores of carbon in the form of coal and oil, which had been captured during previous carbon cycles, and began burning them, releasing the resulting CO2 into our atmosphere far faster than the current cycle can deal with.

最近很多人呼吁大规模植树造林，以捕获大气中的二氧化碳，遏制气候暖化。然而，虽然新生的树木能有效回收和储存碳，但成年老树并非如此。地球本来一直维持着一个平衡的碳循环，树木、以及所有植物和动物，均靠吸收碳而生长，然后枯萎和死亡，将碳再次释放出来。但当人类发现以煤和石油的形式储存的碳，开始燃烧这种石化燃料时，碳循环的平衡就被打破。煤和石油是在远古地质年代在碳循环中被捕获而储藏于地下数以万年的碳，一旦大量开采，燃烧后产生的巨量二氧化碳释放到大气中，其释放速度之快是目前的碳循环无法处理的。

Many pine trees in managed forests, such as the European spruce, take roughly 80 years to reach maturity, being net absorbers of carbon during those years of growth – but once they reach maturity, they shed roughly as much carbon through the decomposition of needles and fallen branches as they absorb. As was the case in Austria in the 1990s, plummeting demand for paper and wood saw huge swathes of managed forests globally fall into disuse. Rather than return to pristine wilderness, these monocrops cover forest floors in acidic pine needles and dead branches. Canada's great forests for example have actually emitted more carbon than they absorb since 2001, thanks to mature trees no longer being actively felled.

在有效管理的森林中，许多松树，如欧洲云杉，需要大约80年才能达到成熟，因此在这80年生长期，是在净吸收碳。不过一旦成年，这些老树开始针叶脱落，树枝枯萎。此时这些树木吸收的碳和释放的碳大致相当。上世纪90年代，对纸张和木材的需求急剧下降，导致全球范围内大片管理森林被废弃，奥地利的森林也出现这样的现象。但这些失去管理的森林没有回复为原始的荒野，森林地下全部覆盖着单一树种的酸性针叶和枯枝。由于成熟的树木无人砍伐制成木材，自2001年以来，加拿大巨大的森林实际排放的碳比吸收的还要多。

Arguably, the best form of carbon sequestration is to chop down trees: to restore our sustainable, managed forests, and use the resulting wood as a building material. Managed forests certified by the Forest Stewardship Council (FSC) typically plant two to three trees for every tree felled – meaning the more demand there is for wood, the greater the growth in both forest cover and CO2-hungry young trees.

此时有人提出一个理论，认为将碳封存起来的最好办法是砍伐树木，恢复可持续的有管理的森林，砍伐成年树木用作建筑材料。经环保团体“森林管理委员会”（FSC）认证的人工管理森林通常每砍伐一棵树就要种植两到三棵树。这意味着对木材的需求量越大，森林的覆盖率和需要呼吸二氧化碳的幼树的增长就越大。

Rewilding and protecting virgin forests is essential. But unmanaged monocrops help no-one, and floors full of dry pine needles are also the primary cause of wildfires – something that North America and many parts of the world experience on a now annual basis. Managed harvesting greatly reduces that risk.

让森林恢复野生和保护原始森林都是必需的。但是，未作管理的单一树种森林则毫无益处，而且这种森林遍地干燥的针叶也是引发野火的主要原因。北美和世界上许多地方都会因此发生这样的森林火灾。有管理的砍伐树木会大大降低这种风险。

These benefits have not been lost on the US authorities. Melissa Jenkins, of the US Federal Forest Service, explained at a recent meeting of the Environmental and Energy Study Institute (EESI), that “we have a situation of overstocked forests: if a wildfire blows through, these fires burn hotter, they burn faster and they take a lot more effort to put out… If we can build markets for these wood products, landowners will be more likely to sustainably manage or sustainably thin their land.” She highlights that CLT in particular as having the potential to reduce “wildfire risk [and] support rural economic development and jobs”.

美国当局对管理森林的好处并非视而不见。在环境和能源研究协会（EES）最近的一次会议上，美国联邦森林管理局的梅丽莎·詹金斯解释说，“我们有森林过密的情况。如果这些森林发生野火，火势会越来越大，燃烧速度会很快，灭火也会更加困难…...如果我们可以为这些森林的木材建立销售市场，森林的业主就可能可持续地管理自己的森林，不时砍伐成树以免森林过密。”她特别强调，交叉层压木板这种工程木料特别有降低“野火风险的潜力，并能支持乡村经济发展和就业”。

The market seems to agree. Less than five years after its arrival on US shores, there are now CLT projects underway in almost every mainland US state. More importantly, unlike the UK – which currently imports all of its CLT – the US is investing in domestic CLT manufacturing, with factories in Montana and Oregon, and more planned in Maine, Utah, Illinois, Texas, Washington State, Alabama and Arkansas. Amazon’s new “tech-hub” building in Minneapolis is made from nail laminated timber (like CLT, but using nails rather than glue). The 2018 Timber Innovation Act also included provisions for research and development into mass timber.

建材市场似乎也同意梅丽莎·詹金斯之说。交叉层压木板登陆美国还不到五年，现在美国几乎每个州都有交叉层压板建筑工程在进行。更重要的是，与目前全部靠进口的英国不同，美国正在投资本国的交叉层压板生产，现设有工厂的有蒙大拿州和俄勒冈州，其余缅因州、犹他州、伊利诺伊州、德克萨斯州、华盛顿州、阿拉巴马州和阿肯色州也计划建厂。亚马逊在明尼阿波利斯新建的“技术中心”大楼是由钉层压木板（类似交叉层压板，但使用钉子而不是胶水来合成多层木板）建成。美国国会通过的《2018年木材创新法案》还包括对大批量木材使用研发的规定。

Structures using wooden materials also tend to be quicker and easier to build, therefore reducing labour costs, transport fuel and on-site energy use. Alison Wring, director of Aecom, an infrastructure company, cites a CLT residential block of around 200 apartments that “took just 16 weeks [to build]… whereas if it had been done traditionally with a concrete frame it would have taken at least 26 weeks.” Similarly, says Waugh, a recent 16,000-square-metre CLT building he worked on, “would have needed around 1,000 cement truck deliveries for the frame alone. To deliver all the CLT, we needed just 92 deliveries.”

使用木材建房会更快、更易建造，因此也减少了劳动成本、运输燃料和建造场地的用电量。基建设施公司Aecom的董事艾莉森·沃林（Alison Wring）以一个使用交叉层压板为建材的住宅屋邨为例。该屋邨约有200套公寓，“只花了16个星期就完工……但要是用上传统的混凝土框架建造，至少需要26个星期”。同样，安德鲁‧沃说，他最近设计的一座一万六千平方米的交叉层压板大楼，如果用混凝土，“仅结构框架就需要1000辆卡车车次来运送水泥”。但运送所有的交叉层压板，“我们只需要92个车次”。

Other countries are turning to timber, too. Monika Lebeničnik, a sales engineer for Ledinek Engineering, an Austrian-Slovenian firm that makes the presses for CLT factories, sent me her order sheet going back to 2013. It begins with a trickle of orders from Austria and Scandinavia. But from 2017 onwards, there is sudden take-up from Japan, France, Australia, Latvia and Canada. “Annual capacity of such lines range from 25,000 to 50,000 cubic meters [of CLT],” explains Lebeničnik. Data suggests that 1,000 cubic metres of CLT equates to around 500 harvested trees; factories processing 50,000 cubic metres are therefore trapping the sequestered carbon of 25,000 trees per year.

其他国家也纷纷转用木材做建材。一家代销交叉层压板的奥地利和斯洛文尼亚合资工程公司Ledinek的销售员莫妮卡，先给我看她公司2013年的订单记录，只有来自奥地利和斯洛文尼亚的少量订单。但从2017年起，日本、法国、澳大利亚、拉脱维亚和加拿大这些国家也纷纷向他们订货。莫妮卡解释说，“我们公司平均每年代销的交叉层压板在2万5千到5万立方米这个范围。”数据显示，1000立方米的交叉层压板相当于要砍伐500棵成年树，因此，每年加工5万立方米的交叉层压板所收回的碳排量就相当于2.5万棵树木所收获的碳。

There are even advantages that make the material particularly attractive to countries like Japan, since it has been found to perform well in earthquake tests. A joint Italian-Japanese research team built a seven-storey CLT building and tested it on a “shake table” (a cool but eerie video of this exists on Youtube). They found that it could withstand shaking at the level of the 1995 earthquake in Kobe, Japan, which destroyed more than 50,000 buildings. With serendipitous timing, says Waugh, “the Americans planted lots of trees in Japan as part of the Marshall Plan – that was over 60 years ago, and they are reaching maturity now”.

交叉层压木板甚至还有一些优势特别吸引日本这样的国家，因为人们发现这种建材在地震测试中表现很良好。意大利和日本的一个联合研究小组曾用交叉层压板建造了一座七层楼房，并在一个“地震模拟台”上进行了测试。Youtube上有这个测试的视频，很酷，但也有点怪异。研究小组发现这座交叉层压板楼房可以承受1995年日本神户地震那样的强度，那次地震摧毁了5万多栋建筑。沃夫说，时间很巧的是，“当年作为马歇尔计划的一部分，美国人在日本种了很多树。那是60多年前的事了，现在这些幼苗已成为参天大树。”

Counterintuitively, CLT also performs well in fires. It is designed to withstand heats of up to 270C before it begins to char – the charring on the outside then acts as a protective layer for the structural density of the wood behind it. By contrast, at similar temperatures concrete can spall and crack, and steel loses its strength.

与人们的直觉相反，交叉层压板抗火能力不但不差，反而相当出色。这种工程建材的设计能够承受高达270摄氏度的高温，然后才开始炭化，而且炭化后的木板外表如同一层保护层，能保护炭化下面的木材结构密度。但在类似的高温下，混凝土会剥落和龟裂，钢也会失去强度。

Not everyone believes that the future is CLT, however. When I ask Chris Cheeseman, professor of materials resources engineering at Imperial College London, whether wood could usurp concrete as our primary building material, his response is blunt. “No. That isn’t going to happen. It might happen locally with some small schemes. But you’ve got to appreciate the massive use of concrete, and the massive importance of concrete to infrastructure and society. It is an exceptionally good material because of its functionality and its robustness.”

不过，并非人人都相信建筑的未来是交叉层压板。我问伦敦帝国理工学院（Imperial College London）材料资源工程学教授克里斯·奇斯曼（Chris Cheeseman），木材能否取代混凝土成为我们的主要建筑材料，他直言回答，“不能。这不会成为现实。只可能用于当地一些小型工程。但你必须认识到混凝土才能大量使用，以及混凝土对基础设施和社会的巨大重要性。因为混凝土的功能性和坚固性，是一种非常好的建筑材料。”

There is also the “end of life” question. Carbon only remains trapped in the wood for as long as the building remains standing or is reused in another building – if it rots or is burned for energy, then all the stored carbon is released. Doug King, a chartered engineer and building sustainability advisor, tells me, “unless we attend to the disposal of timber materials at their end of life there is no guarantee that the overall cycle is making a positive benefit to society.” Previous research work by Arup in 2014 estimated that half of all construction timber ends up in landfill, 36% is recycled and the remaining 14% burnt for biomass energy.

此外，还有一个木材“生命终结”的问题。只要建筑物屹立不倒，或木材料回收后用于其他建筑，碳就会一直被困在木材里。但如果木材腐烂或者作为能源被燃烧，那么储存在木材中的碳就会被释放到大气中。特许工程师、建筑可持续发展顾问道格·金（Doug King）告诉我，“除非我们能解决木材使用寿命结束后的处理问题，否则无法保证木材的整个碳循环过程会有益于社会。”英国奥雅纳建筑公司于2014年做的研究估计，一半的建筑木材最终被填埋，36%被回收，剩下的14%会作为生物质能源使用。

Despite these issues, Waugh remains ambitious. The average lifetime of a building is 50-60 years – that, he believes, is more than enough time for architects and engineers to work out the re-use and recycling issues. Turning it into biochar could be one possibility. Waugh’s buildings are made to be easy to take apart for re-use by future generations.

虽然有这些问题，但仍然未能阻止安德鲁‧沃开发木结构建筑的雄心壮志。一座建筑的平均寿命是50至60年。他认为，五六十年时间足够建筑师和工程师解决再利用和回收问题。转化为生物炭或许是一种选择。因此他的建筑事务所所设计的建筑都易于拆卸，其材料可供后代子孙一用再用。

Fundamentally he – along with a growing group of international architects – is convinced that mass adoption of CLT is an important weapon in the fight against climate change. “It’s not a fad or a fashion,” he tells me as we finish the tour of his east London build, and I take my final, incongruous breath of the forest air. “The largest commercial developer in the UK have just bought this building. For me, that’s where you want to be… I want this to be mainstream. Everybody should be building with this.”

基本而言，安德鲁‧沃与越来越多的国际建筑师相信，大规模使用交叉层压板作建材是对抗气候变化的一个重要武器。参观完东伦敦这座正在动工的交叉层压板楼房，再次深深呼吸一下这来自森林的气味后，沃对我说，“这不是什么短期或长期的时尚。英国最大的商业开发商刚刚买下了这栋楼房。对我来说，这就是你想要的居住的环境…...我希望交叉层压木板成为主流建材。大家都应该用来建房。”

I return to my original question: could we realistically return to wood as our primary building material? “It’s not only realistic, it’s imperative,” argues Waugh. “It has to happen. In architecture you always go back to the sketch: the sketch is climate change.”

我再提到我最初的问题：我们是否可以真正地将木材作为人类的主要建筑材料？沃这样回答：“这不仅是可行的，而且势在必行。我们必须这样做。说到建筑，你一定要先制作草图，而草图就是气候变化。”