Can you rule out all other options, both known and unknown, both probable and implausible? You can't; ergo, you "can't" conclude the house was designed, unless the designer himself stands up and claims. (Which he does, because construction firms advertise.)
What if we are the designers, and are not standing up? Instead living a lie, acting (with conviction) in irresponsible fashion?
Does science / scientific method have intelligent designer? Or plausible that original designer is nowhere to be found and it is random occurrence within pattern of philosophy?
Where is the tangible evidence that our methodologies are intelligent? I mean the objective evidence (apart from our obvious bias).